Fix the empty checkpoint timeout.

The problem happens when a thread is indirectly blocked on a mutex
that another thread holds and is blocked on a weak ref access.

Add a way to do a dummy wakeup on a thread that's blocked on a mutex
so that the thread will respond to the empty checkpoint request. Do
this for the mutexes that are expected to be held when a weak ref is
accessed. Add a check that detects an unexpected case.

Bug: 33006388
Bug: 12687968
Test: test-art-host.
Change-Id: Iefec69b9a21aa25a928cb31fcf4fb872f867a8c2