[A11y Focus API] Add new requestRectangleOnScreen API with a parameter for source

* See go/android-a11y-focus-api for full justification and design.
* Support differentiating calls to requestRectangleOnScreen using
  a parameter for the source type.
* Add the new API to View behind a flag.
* Update original API to call new API with UNDEFINED for backward compat.
* Update View#onFocusChanged to call this new API behind the flag.
* Update TextView#bringPointIntoView to call this new API behind the flag.
* Update intermediate layers to plumb the source value up to
  AccessibilityController.

Flag: android.view.accessibility.request_rectangle_with_source
Bug: 391877896
Bug: 393192321
Bug: 393193738
Bug: 393194121
Test: cts/.../ViewTest.java, cts/.../TextViewTest.java
Change-Id: I584203459a54412aa816ed769b507864f50a49ee