Avoid ambiguous overload of HashMap.get for types that implicitly cast from const to non-const.
Implement the draft of a new task local storage facility.

Still missing:
 - destroy fiber local storage after each task exists
 - handle alignment properly
 - testing!
Fix compilation of non-debug builds.
Remove high-frequency log output in critical places.

"Critical place" meaning places where a logger that itself yields could cause strange effects/errors.
Remove high-frequency log output.
Various improvements.

 - Add TaskEvent.postStart
 - Add a Fiber parameter to the setTaskEventCallback
 - Make TaskLocal work when called from outside of a task
 - Remove high-frequency log output
Just create the global dummy CoreTask lazily.