Document core locking principles

[q2333gh]

Summary

• add English documentation of the core locking approach, key Win32 APIs, and watchdog safeguards for ShowWhatProcessLocksFile so readers can understand the implementation without reading the code

Testing

• not run

[PolarGoose]

Thanks a lot for the pull request. Yes, it is a good idea to document it, because it is really some kind of magic. Unfortunately, there is just no way to make the implementation simpler.

I will look into that in a couple of days.