[llvm] [clang] Setup whitespace detection and clang-format as Github actions (PR #66509)

[Tobias Hieta via llvm-commits]

tru wrote:

@ldionne thanks for the whitespace check! I have already put some work into the clang-format action on my end. Would you mind dropping it from this PR and let me push mine first? My action is not just restricted to the clang subdir. 

https://github.com/llvm/llvm-project/pull/66509