[GR-71896] The error codes that `graal_create_isolate` can return should be documented

[mikehearn]

The docs for graal_create_isolate are not very helpful with respect to errors:

Create a new isolate, considering the passed parameters (which may be NULL).
Returns 0 on success, or a non-zero value on failure.

The errors it can return are documented internally here:

https://github.com/oracle/graal/blob/master/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/c/function/CEntryPointErrors.java

But the docs of that class say it's internal API.

One or both of the following would be useful:

1. A graal_error_code_to_string function that returns the @Description for an error code.
2. Documentation that explains each (common) error code the user may encounter.