Unbind InputMethod when app crashes

If a running app (with bound InputMethod) crashes, the currently running InputMethod is not
unbound. As a result, onBindInput is not called.
In order to fix this, IMMS.removeClient() should also unbind the current client and clear
the flag IMMS.mBoundToMethod.
With the fix, I haven't seen any test failures mentioned in bug.

Bug: 72399950
Fixes: 73274813
Test: atest InputMethodServiceLifecycleTest && atest FocusHandlingTest
Change-Id: I0c09381b43a8b96480976edafbc0b0ee40ae5de0