PydanticKnownError should not drop custom user error context

[davidhewitt]

See #809 (comment)

Selected Assignee: @lig

[davidhewitt]

cc @MarkusSintonen I created this issue for us to remember to revisit this following the merge of #809

[MarkusSintonen]

@davidhewitt I have a fix done, but it required changing the ErrorType and the associated macros so the enum is able to carry context (and not just the specific whitelisted fields). At first I though it might be possible to carry the context in struct PydanticKnownError-field but it wouldnt work as the custom context is again lost as the ErrorType-enum is the one that internally carries the error data (eg when raising PydanticKnownError in validator its internally converted to ErrorType).

What do you think, does the approach sound solid to extend the ErrorType so all enums include possibly custom context? Inclusion of the common field for the enum items requires changing the macros to do it.

[MarkusSintonen]

Btw doing above also fixes this issue where the given type is lost on the way: https://github.com/pydantic/pydantic-core/blob/main/tests/test_errors.py#L332-L335 So there given Decimal would stay as Decimal

[MarkusSintonen]

Opened the fix: #839