Do not enter touch mode on non-touchscreen events

Currently ACTION_DOWN and ACTION_SCROLL cause
entering touch mode regardless of the event source.
This is especially awkward for mouse.

This should only happen when the event source is
SOURCE_TOUCHSCREEN.

Bug: 35314124
Test: android.cts.view.ViewTest#testTouchMode
Change-Id: I2205d4240be4afcbd9a3ac5558e701f7cac51926