Fix the multi-fingers gesture conflict with TouchExplorer

TouchExplorer supports multi-finger gestures from R. However,
FullScreenMagnificationGestureHandler has higher priority of
receiving motion events than TouchExplorer. When the screen is
zoomed in, two pointersdown gesture makes it transiting to
PanningScalingState.

To fix it, We post a tap tmeout to transit to PanningScalingState
when receiving two pointers down. In this duration, any pointers
action will make it transiting to DelegatingState. We also add
a condition that is if the movement of any fingers exceeed the
touchSlope, it will transit to PanningScalingState.

Bug: 159508732
Test: atest FullScreenMagnificationGestureHandlerTest
atest MagnificationGestureHandlerTest

Change-Id: Ic72c0da68a6a4f1714da8d05f743d6218793a5da