Gesture detection for window magnification (1/n)

To change the gesturehandler easily for different magnification mode,
we rename MagnificationGestureHandler to FullScreenMagnificationGestureHandler
and add a common class MagnificationGestureHandler. We will create
different MagnificationGestureHandler based on magnification mode.

Bug: 146400227
Test:FullScreenMagnificationGestureHandlerTest
Test: AccessibilityInputFilterTest.java
Change-Id: Ib7a45300a1f1323e1005b89694bb66932b22ab1b