MotionEvent: add test API to identify resampled events

The VirtualTouchscreenTest#sendTouchEvent CTS test injects input events
and checks that they are delivered to an app correctly. However, we
think that performance issues in the test device fleet sometimes cause
these events to be delivered so slowly that they end up being resampled,
causing the test's assertions to fail. Exposing this API allows the test
to ignore resampled events.

I can't just make the raw field visible (like the others are), as
metalava complains if I do so.

Bug: 292544797
Test: see the CTS CL
Change-Id: I553d1daba65f1d9886cc778d4ac4bdccc29954b7