[clang] [libcxx] [clang][ThreadSafety] Handle mutex scope (PR #157171)

[Aaron Puchert via cfe-commits]

aaronpuchert wrote:

Commented on #156760: the issues is that we don't support scoped lockable arguments for the attributes. (That is, we support a different syntax since #110523, but we can't use that for `std::lock` which accepts both lockable and scoped lockable arguments, possibly even mixed.)

https://github.com/llvm/llvm-project/pull/157171