[RFC][libc++] Reworks clang-tidy selection. (#81362)

The current selection is done in the test scripts which gives the user
no control where to find clang-tidy. The version selection itself is
hard-coded and not based on the version of clang used.

This moves the selection to configuration time and tries to find a
better match.
- Mixing the version of clang-tidy and the clang libraries causes ODR
violations. This results in practice in crashes or incorrect results.
- Mixing the version of clang-tidy and the clang binary sometimes causes
issues with supported diagnostic flags. For example, flags tested
against clang 17 may not be available in clang-tidy 16.

Currently clang-tidy 18.1 can be used, it tests against the clang
libraries version 18. This is caused by the new LLVM version numbering
scheme.

The new selection tries to match the clang version or the version of the
HEAD and the last 3 releases. (During the release period libc++ supports
4 versions instead of the typical 3 versions.)