Handles magnification scale change when requesting Accessibility action

The magnification sale should be consistent between a11y framework
and systemUi. So when a user requests to perfom scale a11y action by
systemUi, We need to handle it in Framework to ensure consistency
of the magnification scale.

Bug: 170791657
Test: atest WindowMagnificationTest WindowMagnificationManagerTest
WindowMagnificationControllerTest MagnificationControllerTest
Change-Id: Iaa34e66f29b320be971d416ce38d770b2265915f

Change-Id: I0598accefd62a8cefd93bda6163ac704fdd96cba