New C/Py api utility function PyC_Err_Format_Prefix() which raises an error with the existing error as a suffix.

Use this to raise errors when assigning a string property fails even though the value to assign *is* a string.


Before:
  TypeError: bpy_struct: item.attr= val: Object.name expected a string type, not str


After:
  TypeError: bpy_struct: item.attr= val: Object.name error assigning string, UnicodeEncodeError('utf-8' codec can't encode character '\udce9' in position 23: surrogates not allowed)

source/blender/python/generic/py_capi_utils.h

@@ -34,6 +34,7 @@ void			PyC_ObSpit(const char *name, PyObject *var);
 void			PyC_LineSpit(void);
 PyObject *		PyC_ExceptionBuffer(void);
 PyObject *		PyC_Object_GetAttrStringArgs(PyObject *o, Py_ssize_t n, ...);
+PyObject *		PyC_Err_Format_Prefix(PyObject *exception_type_prefix, const char *format, ...);
 void			PyC_FileAndNum(const char **filename, int *lineno);
 int				PyC_AsArray(void *array, PyObject *value, const int length, const PyTypeObject *type, const short is_double, const char *error_prefix);