Implement transitn animation while switching the mode

First we get the current center of magnification bounds and the scale,
then apply them after the disabling animation is completed.

If disabling animation is interrupted, we will fall back to previous
mode or force to switch the mode directly.

Bug: 161669184
Test: atest com.android.server.accessibility.magnification
      atest AccessibilityManagerServiceTest
Change-Id: Ic12d6d907f91bf251aa67a6ab959d4fbcf660f63