MotionEvent: Simplify logic around transformations

This is a refactor that simplifies logic around Transforms applied to
MotionEvents.

PointerCoords should only contain raw values that are unmodified by
MotionEven transformations. The MotionEvent's Transform should only be
applied when getting these values through MotionEvent's getAxisValue
APIs.

Bug: 179274888
Test: atest libinput_tests
Test: manual with test app
Change-Id: If60d98ade84d481afd655a3abc921e50697071b3