'ClsClassImpl' instances created by the platform contain synthetic
enum methods (added by 'ClassInnerStuffCache.calcMethods()'). Such
convention is common in IntelliJ (see KT-36095 and
'9a8b345adaded83fe13980a28db5d9f9acc7450d' in the IntelliJ repository).
This commit makes Kotlin's stub-based classes consistent with the
convention. Instead, a filter is added in place of 'ClsClassImpl' usage.
See also the following commits:
- 7c86911f44
- 43468c6d55