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

[Henrik G. Olsson via cfe-commits]

hnrklssn wrote:

> >  The ; did you mean to use BAR? version was accidentally emitted in some cases where it didn't make sense to do so, but the tests still passed because the diagnostic did contain cannot use FOO in context asdf.
> 
> 
> 
> There's a `FileCheck` flag to enforce this: `--match-full-lines`

Clang diagnostic tests don't use FileCheck, instead clang has a -verify flag.

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