[clang] [BoundsSafety] unify ParseLexedAttribute (PR #186033)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Agree with Corentin's suggestions on shrinking the patch a little.  I've a preference for `HasFuncScope` instead of `HasFunScope` (the former is MUCH less... ambiguous to read), otherwise I'm happy  when Corentin is.

https://github.com/llvm/llvm-project/pull/186033