Verify KeyEvents in IME

Malicious app can inject fabricated InputEvents into IME's FD which can
do tinker with special shortcuts like switching IME.
With this CL, all KeyEvents with modifiers OR indicated sensitive by IME will be
verified before being dispatched to IME.

For any events that are replayed, verify timestamp.

Bug: 331730488
Test: atest CtsInputMethodTestCases InputMethodServiceTest
Flag: android.view.inputmethod.verify_key_event

Change-Id: Ice0632c3e39892772f2931aea38b5db694df4423