display an error when attempting to rename a symbol to an invalid python identifier

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from #1506

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Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
-   .../projects/sympy/sympy/sets/handlers/functions.py:173:5 - warning: Type of "F" is unknown (reportUnknownVariableType)
+   .../projects/sympy/sympy/sets/handlers/functions.py:173:5 - warning: Type of "F" is partially unknown
+     Type of "F" is "Unknown | Expr | Any | Piecewise | Self@Add" (reportUnknownVariableType)
-     Argument corresponds to parameter "args" in function "imageset" (reportUnknownArgumentType)
-   .../projects/sympy/sympy/sets/handlers/functions.py:175:28 - warning: Argument type is unknown
-     Type of "set_mul" is "(x: Unknown, y: Unknown) -> (Any | Unknown | FiniteSet | ImageSet)" (reportUnknownVariableType)
+     Type of "set_mul" is "(x: Unknown, y: Unknown) -> (Any | Unknown | FiniteSet | ImageSet | Union)" (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/handlers/mul.py:64:5 - warning: Return type, "Unknown | FiniteSet | Interval | Any | ImageSet", is partially unknown (reportUnknownParameterType)
+   .../projects/sympy/sympy/sets/handlers/mul.py:64:5 - warning: Return type, "Unknown | FiniteSet | Interval | Any | ImageSet | Union", is partially unknown (reportUnknownParameterType)
-   .../projects/sympy/sympy/sets/handlers/mul.py:79:12 - warning: Return type, "Any | Unknown | FiniteSet | ImageSet", is partially unknown (reportUnknownVariableType)
+   .../projects/sympy/sympy/sets/handlers/mul.py:79:12 - warning: Return type, "Any | Unknown | FiniteSet | ImageSet | Union", is partially unknown (reportUnknownVariableType)
-     Type of "set_div" is "(x: Unknown, y: Unknown) -> (Any | Unknown | FiniteSet | ImageSet)" (reportUnknownVariableType)
+     Type of "set_div" is "(x: Unknown, y: Unknown) -> (Any | Unknown | FiniteSet | ImageSet | Union)" (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/ordinals.py:18:13 - warning: Type of "a" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:123:9 - warning: Return type is unknown (reportUnknownParameterType)
-   .../projects/sympy/sympy/sets/ordinals.py:128:9 - warning: Return type, "_NotImplementedType | Unknown | bool", is partially unknown (reportUnknownParameterType)
-   .../projects/sympy/sympy/sets/ordinals.py:131:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:134:16 - warning: Return type, "Unknown | bool", is partially unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/ordinals.py:134:30 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:142:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:145:54 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:145:54 - warning: Argument type is partially unknown
-     Argument corresponds to parameter "iter2" in function "__new__"
-     Argument type is "Unknown | tuple[Basic, ...]" (reportUnknownArgumentType)
-   .../projects/sympy/sympy/sets/ordinals.py:148:38 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:148:38 - warning: Argument type is partially unknown
-     Argument corresponds to parameter "obj" in function "len"
-     Argument type is "Unknown | tuple[Basic, ...]" (reportUnknownArgumentType)
-   .../projects/sympy/sympy/sets/ordinals.py:185:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:191:24 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:191:24 - warning: Argument type is partially unknown
-     Argument corresponds to parameter "iterable" in function "__init__"
-     Argument type is "Unknown | tuple[Basic, ...]" (reportUnknownArgumentType)
-   .../projects/sympy/sympy/sets/ordinals.py:199:60 - warning: Type of "leading_term" is partially unknown
-     Type of "leading_term" is "Unknown | Basic" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:205:9 - warning: Return type, "_NotImplementedType | Unknown | Ordinal", is partially unknown (reportUnknownParameterType)
-   .../projects/sympy/sympy/sets/ordinals.py:208:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:211:16 - warning: Return type, "Unknown | _NotImplementedType | Ordinal", is partially unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/ordinals.py:216:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:224:12 - warning: Type of "is_limit_ordinal" is partially unknown
-     Type of "is_limit_ordinal" is "Unknown | bool" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:225:17 - warning: Type of "arg" is partially unknown
-     Type of "arg" is "Unknown | Basic" (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/ordinals.py:225:24 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:229:17 - warning: Type of "arg" is partially unknown
-     Type of "arg" is "Unknown | Basic" (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/ordinals.py:229:24 - warning: Type of "terms" is partially unknown
-     Type of "terms" is "Unknown | tuple[Basic, ...]" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:231:22 - warning: Type of "trailing_term" is partially unknown
-     Type of "trailing_term" is "Unknown | Basic" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:236:9 - warning: Return type, "_NotImplementedType | Unknown | OrdinalZero | Ordinal", is partially unknown (reportUnknownParameterType)
-   .../projects/sympy/sympy/sets/ordinals.py:239:17 - warning: Type of "other" is unknown (reportUnknownVariableType)
-     Type of "convert" is "(integer_value: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "convert" is "(integer_value: Unknown) -> (OrdinalZero | Ordinal)" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/ordinals.py:242:16 - warning: Return type, "Unknown | _NotImplementedType | OrdinalZero | Ordinal", is partially unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/sets.py:1079:9 - warning: Type of "left_open" is unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/sets.py:1080:9 - warning: Type of "right_open" is unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/sets.py:1083:17 - warning: Type of "a" is unknown (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:143:5 - warning: Type of "S1" is partially unknown
-     Type of "S1" is "Unknown | Basic | ImageSet | FiniteSet" (reportUnknownVariableType)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:144:12 - warning: Type of "base_pset" is partially unknown
-     Type of "base_pset" is "Unknown | FiniteSet | ProductSet" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:144:15 - error: Cannot access attribute "base_pset" for class "Basic"
-     Attribute "base_pset" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:144:15 - error: Cannot access attribute "base_pset" for class "FiniteSet"
-     Attribute "base_pset" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:145:12 - warning: Type of "base_sets" is partially unknown
-     Type of "base_sets" is "Unknown | Any" (reportUnknownMemberType)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:145:15 - error: Cannot access attribute "base_sets" for class "Basic"
-     Attribute "base_sets" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/sets/tests/test_fancysets.py:145:15 - error: Cannot access attribute "base_sets" for class "FiniteSet"
-     Attribute "base_sets" is unknown (reportAttributeAccessIssue)
+   .../projects/sympy/sympy/simplify/fu.py:492:20 - warning: Argument type is unknown
+     Argument corresponds to parameter "rv" in function "TR8" (reportUnknownArgumentType)
+   .../projects/sympy/sympy/simplify/radsimp.py:1017:9 - warning: Type of "n" is unknown (reportUnknownVariableType)

... (truncated 90 lines) ...