Fix: Potential race condition fix for systemUI crash in KGC

Rapid restart of systemUI after a crash causes it to call KGC
registerKeyGestureHandler while the old binder hasn't been cleaned
up (linkToDeath() callback hasn't occured). It is possible that
isBinderAlive() call that uses internal state hasn't yet received
the "death" information.
So, deliberately call "pingBinder" to see if the old binder is
alive and cleanup old handler (if register call comes before the
cleanup has occurred).

Bug: 414477543
Test: manual
Flag: EXEMPT bugfix
Change-Id: If743855b4c4f9b0feb9f947a89044a7c67fc07ab