Methods `needToGenerateAdditionalMembersInClass` and
`needToGenerateNestedClassifiersInClass` are removed, now compiler
uses `get...Names` and `getTopLevel...` methods to determine which
extension may generate declaration with specific classId/callableId
This is needed to simplify API of FirDeclarationGenerationExtension and
provide guarantee that `generate...` method will be called with
specific classId/callableId only if specific extensions returned name
for this id from `getName...` functions