cherry-pick macOS OSSpinLock replacements

This popped up todaY: https://hacks.mozilla.org/2022/10/improving-firefox-responsiveness-on-macos/

These patches landed in Firefox 103:

• Bug 1670885: Replace deprecated OSSpinLock with os_unfair_lock

  • f56fb962 : Fix post-fork() handlers for PHC/LogAlloc to work on macOS using unfair locks
  • 8f9904bb : Replace deprecated NSSpinLocks with os_unfair_locks in the memory allocator

• Bug 1774458: Use undocumented, non-public adaptive spinlocks on macOS 10.15+, revert to user-space spinlocks on older versions

  • 7e8fda1a : Use undocumented, non-public adaptive spinlocks on macOS 10.15+, revert to user-space spinlocks on older versions

and this in 106:

• Bug 1784018: Remove deprecated OSSpinLocks
  • 44cbaf42 : Remove deprecated OSSpinLocks

We should see if these apply cleanly and consider cherry-picking to alpha (esr102)