[clang-tools-extra] [clang-tidy][NFC] Run tests in multiple language modes where possible (PR #184741)

[Carlos Galvez via cfe-commits]

carlosgalvezp wrote:

Should this be added to the documentation about writing clang-tidy checks and/or the script that generates the check skeletton?

It also feels like the wrong default. If I write `-std=c++14` the test runner should turn that into `c++14-or-later`, and only if I really want only one standard, I should write `-std=c++14-only`.

https://github.com/llvm/llvm-project/pull/184741