Re-implement full screen magnification continuous cursor following

This migrates an existing full screen magnification's continuous cursor
following feature to use AccessibilityPointerMotionFilter so that other
types of cursor following features can be implemented similarly.

Bug: 361817142
Test: FullScreenMagnificationControllerTest
Test: FullScreenMagnificationGestureHandlerTest
Test: FullScreenMagnificationPointerMotionEventFilterTest
Flag: com.android.server.accessibility.enable_magnification_follows_mouse_with_pointer_motion_filter
Change-Id: I482c121cbc0d1da64e6d22aabcc3894caf89bb18