[Clang] Fix Sema::ClassifyName so that it classifies EnumConstantDecl as...

[Clang] Fix Sema::ClassifyName so that it classifies EnumConstantDecl as NonType when they are brought into scope via using enum

Currently Sema::ClassifyName(...) in some cases when an enumerator is brought
into scope via using enum during lookup it can end up being classified as an
OverloadSet. It looks like this was never accounted for when using enum support
was implemented and we need to add a check to allow an EnumConstantDecl to be
classified as NonType even when it is a class member.

This fixes:
  https://github.com/llvm/llvm-project/issues/58057
  https://github.com/llvm/llvm-project/issues/59014
  https://github.com/llvm/llvm-project/issues/54746

Differential Revision: https://reviews.llvm.org/D138091