sanitizer_common: rename Mutex to MutexState

We have 3 different mutexes (RWMutex, BlockingMutex __tsan::Mutex),
each with own set of downsides. I want to unify them under a name Mutex.
But it will conflict with Mutex in the deadlock detector,
which is a way too generic name. Rename it to MutexState.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D105773