✨ Add RecursiveMutex class & make Mutex/RecursiveMutex ctors constexpr

[ion098]

Summary:

Adds a RecursiveMutex class, and make the constructors for Mutex/RecursiveMutex constexpr.

Motivation:

There is currently no C++ API for recursive mutexes, which prevents using std::lock_guard with recursive mutexes. Making the constructors constexpr allows mutex variables to be declared as constinit.

Test Plan:

• Check that it compiles.
• Check that the mutex only allows one thread to lock it.
• Check that the same thread can lock the RecursiveMutex multiple times.

[Rocky14683]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).