Add WindowMagnificationBridge for animation

WindowMagnificationBridge provides same functionality
but it runs the animation while enabling/disabling.

Bug: 161669184
Test: atest com.android.systemui.accessibility
atest WindowMagnificationGestureHandlerTest
       manual Test: enable window magnification to see it

Change-Id: Ifdedff335e856ba12209883924032aa545d04738