[clang] [clang][ThreadSafety] Warn when constructor is trylock (PR #95290)

[Dan McArdle via cfe-commits]

dmcardle wrote:

Just force-pushed what I described in the last comment.

1. Changed void-returning trylock functions to return bool in tests. (Probably needs another pass to minimize the diff and undo some unnecessary changes.)
2. Now enforcing bool/int/pointer returns from trylock-annotated functions.
3. Also updated the Thread Safety Analysis doc a bit.

PTAL. Thanks!

https://github.com/llvm/llvm-project/pull/95290