[A11y Focus API] Update Magnification to use requestRectangleOnScreen API with source

* See go/android-a11y-focus-api for full justification and design.
* Update Magnification to respect the new parameter to the
  requestRectangleOnScreen API behind the flag.
* Update Magnification to differentiate between typing and keyboard
  focus events and move the viewport accordingly.
* Set Magnification follow keyboard focus default to false.
* Update and add unit tests to test both unflagged and flagged
  behavior.

Flag: android.view.accessibility.request_rectangle_with_source
Bug: 391877896
Bug: 391678911
Bug: 391679180
Test: FullScreenMagnificationControllerTest.java,
MagnificationConnectionManagerTest.java, MagnificationControllerTest.java

Change-Id: Iad4ae9800afc9053d6f1c84d79572b9e58b56272