[clang-tools-extra] [clang-tidy] Add parallel execution by default in 'run-clang-tidy' and 'clang-tidy-diff' (PR #149739)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> Also I think `clang-tidy-diff.py` should refer to Clang-Tidy. Several places are affected.

Do you mean renaming `clang-tidy` -> `Clang-Tidy` in scripts output/docs?

https://github.com/llvm/llvm-project/pull/149739