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

[Tarun Prabhu via cfe-commits]

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

Thanks. Since flang shares the driver, this makes the code a bit less surprising on the flang side.

As @kiranchandramohan said, please wait till you get approval from the clang code owners and maintainers.

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