InputDispatcher: Only send touchpad nav gestures to trusted overlays

Because we don't want apps using the touchpad navigation gestures (at
the moment, any swipes with three or more fingers), we need to only send
them to system UI windows. For now, determine this by checking for the
TRUSTED_OVERLAY InputConfig flag.

Bug: b/279803433
Test: atest inputflinger_tests
Test: check that no events are sent to a test app when making three- or
      four-finger swipes on a touchpad
Change-Id: I0830cb37d1ed615df0d6c546f1febbac89bab410