Fix unexpected IME show because of stale requestedVisibleAwaitingControl

Fixes an issue where the IME would unexpectedly open whenever the
controls change because requestedVisibleAwaitingControl might
be stale.

To fix this, we clear the flag whenever it has been applied after
gaining control, when we hide the IME.

Fixes: 181218935
Test: atest 'WindowInsetsControllerTests#testShowImeOnCreate_doesntCauseImeToReappearWhenDialogIsShown'
Change-Id: I251707fc72c908829f2e69d5b1667e71123fbd0f