gh-111924: Use PyMutex for Runtime-global Locks. (gh-112207)

gh-111924: Use PyMutex for Runtime-global Locks. (gh-112207)

This replaces some usages of PyThread_type_lock with PyMutex, which does not require memory allocation to initialize.

This simplifies some of the runtime initialization and is also one step towards avoiding changing the default raw memory allocator during initialize/finalization, which can be non-thread-safe in some circumstances.