[clang] Reland "[Utils] add update-verify-tests.py" (#108630)" (PR #108658)

[Erich Keane via cfe-commits]

erichkeane wrote:

As a CFE reviewer, I very much hate the existence of this script (and the CodeGen equivalents, but that is a separate discussion).

This existing means I can no longer trust that a test is a reflection of what the author intended to write, as they might have just run this and "YOLO'ed" it away.  So now I have to be 100x more careful reviewing tests, which means significantly worse review bandwidth.  This is the same problem I have with AI generated code/tests, as this is basically only a 1/2 step above, "Hey Google, write me a lit test for this".

@cor3ntin and @AaronBallman and @Endilll .

https://github.com/llvm/llvm-project/pull/108658