Reject invalid events injected by accessibility

This will avoid the processing of inconsistent event streams inside
dispatcher, which can lead to crashes. Going forward, we should reject
all inconsistent injected events, not just those from a11y.

Bug: 356662669
Flag: EXEMPT bugfix
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="*InvalidA11yEventsGetRejected"
Change-Id: Ia127bcedf2288a2522d33d046fbbc8eb389babfb