Use pointer source in MotionEventTest#testEventRotation

Only pointer sources have event rotation applied to them by MotionEvent.
We need to a pointer source like SOURCE_TOUCHSCREEN to ensure the event
is rotated as expected.

Bug: 179274888
Test: atest MotionEventTest

Change-Id: I610858c50bfbd42ecfeb326d162b17a3cb93f544