Change condition for entering in touchMode

Currenly when motionEvent is injected,
current logic makes touchmode false even if the event's source is STYLUS or MOUSE event,
which seems not an intended behavior that leaving touchMode.

Hence, modify the logic to make sure touchMode is ture only when event source is TOUCHSCREEN.

Bug: b/135752906
Test : run android.view.cts.ViewTest#testTouchMode
(cherry picked from commit 12b99ea7f108ec3b240f6bd569a5c6ab0f925071)