[clang-tools-extra] [clang-tidy] add modernize-use-constexpr check (PR #146553)

[Baranov Victor via cfe-commits]

https://github.com/vbvictor commented:

Gave this a very rought look, so only a couple of general questions/suggestions.

Could we do something with methods that repeat in some of the visitors, e.g. `bool TraverseType(QualType QT)` and others. Maybe macros..? I can't think of a better idea right now.

Could we break this PR in multiple ones, e.g. first with support of CXX11, then CXX14 and so on? 1000-line `.cpp` file is hard to review. Also, with a PR for each standart we will understand better what changed and what new constexpr cases appear.

https://github.com/llvm/llvm-project/pull/146553