[clang-tidy][request] Check that detects unqualified enumerator usage

```c++
enum E { E0, E1 };
E f(E e) {
if (e == E0) {} // warn
return E::E1; // ok
}
```
Use cases: C++ code using C headers, preparation of switch to `enum class`, improve readability.

Start by locating the clang-tidy check entry points and nearby check tests, then compare the supplied C++ example with existing diagnostics. The work is done when unqualified enumerator use such as E0 is diagnosed while qualified use such as E::E1 is accepted, with coverage for the stated C++ header and enum-class migration use cases.

Written by the indexing model from the issue text.