[Local GC] Break EE dependency on GC's generation table and alloc lock in single...

[Local GC] Break EE dependency on GC's generation table and alloc lock in single-proc scenarios (#10065)

* Remove usage of the generation table from the EE by introducing an
EE-owned GC alloc context used for allocations on single-proc machines.

* Move the GC alloc lock to the EE side of the interface

* Repair the Windows ARM build

* Move the decision to use per-thread alloc contexts to the EE

* Rename the lock used by StartNoGCRegion and EndNoGCRegion to be more indicative of what it is protecting

* Address code review feedback 2 (enumerate the global alloc context as a part of GCToEEInterface)

* Code review feedback (3)

* Address code review feedback (move some GC-internal globals to gcimpl.h and gc.cpp)

* g_global_alloc_lock is a dword, not a qword - fixes a deadlock

* Move GlobalAllocLock to gchelpers.cpp and switch to preemptive mode when spinning

* Repair the Windows x86 build