a11y: add zoomInFullScreenMagnification method in MagnificationController

* This CL addresses the scenario where the key gesture first time
  confirmation dialog is shown for Magnification. When the dialog pops
up, we should perform the zoom in action with persisted scale.
* This CL adds a method in MagnificationController to activate the
  fullscreen magnification and zoom in with persisted scale.

Bug: b/425722546
Flag:com.android.hardware.input.enable_magnify_magnification_key_gesture_dialog
Test: manual & atest MagnificationControllerTest,
MagnificationConnectionManagerTest

Change-Id: I8e19da5622591a8b8bc3fe35d4acb38ae04b422f