Make MotionEvent.getEventTimeNano API public.

We need a nanosecond precision for the resampling algorithm in Chrome.
Currently we use a reflection to access these methods
https://crrev.com/c/4282897, but we get an approval to make these
methods public.

Test: atest cts/tests/tests/view/src/android/view/cts/MotionEventTest.java

Bug: b/269238283

Change-Id: I2ac814e777ab954268a450987d11481e6bd32ff9