* [ASRunLoopQueue - Performance] Add ASDeallocQueue for efficient object teardown.
This measurably reduces block overhead and context switching. In the layout benchmark,
it increases ops/s while actually reducing CPU utilization. This suggests that we are
now at a lock-bounded local maximum, at least for tri-core devices.
* [ASDeallocQueue] Update convenience helper method and adopt in ASImageNode etc.
* [ASDeallocQueue] Reimplement the queue using a timer-based runloop.
* [Debugging] Re-enable ASDisplayNode Event Log.
* [ASDeallocQueue] Final refinements, comments, code minimization.
* [ASDeallocQueue] Fix for lock release needed in early return (refactoring typo from last commit)
* [Debugging / Profiling] Add kdebug_signpost calls to Range and DataController.
* [ASLog] Add new ASProfilingSignpost defines for System Trace flags.
* [ASLog] Improve kdebug_signpost logging: ASRunloopQueue and AsyncDisplay, and colors.
See https://github.com/facebook/AsyncDisplayKit/pull/2370 for screenshots.
We don't nee CFRunLoopWakeUp as at this time are currently running in an observer callback, and after running all of the BeforeWaiting observers it must surely check for more sources / etc to run before determining if it will sleep
It is not guaranteed that the runloop will turn if it has no scheduled work, and this causes processing of the queue to stop. Attaching a custom loop source to the run loop and signal it if new work needs to be done
