[clang] [Clang] skip shadow warnings for enum constants in distinct class scopes (PR #115656)

[Michael Jabbour via cfe-commits]

michael-jabbour-sonarsource wrote:

Hello,

I think that the following cases used to be valid reports on clang 19, but they are not reported in clang 20 after this patch. Is this intended?

```cpp
namespace classEnums {
int globalVar = 0;
class ClassWithEnum {
  enum Enum {
    globalVar  // No -Wshadow after this patch.
  };
};

class OuterClass {
  static const int memberData = 0;
  enum Enum {
    enumVal
  };
  class InnerClass {
    enum Enum {
      memberData,  // No -Wshadow after this patch.
      enumVal  // No -Wshadow after this patch.
    };
  };
};
}
```
CE: https://godbolt.org/z/no87EEYxn

@a-tarasyuk, @Fznamznon, @Sirraide

https://github.com/llvm/llvm-project/pull/115656