[clang] [clang][driver] Rename ClangExecutable and getClangProgramPath (NFC) (PR #200814)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

Seems fine, since we do share it. I can also see it disambiguating between `clang` and `clang -cc1`.

https://github.com/llvm/llvm-project/pull/200814