Support for OnBackAnimationCallback: added for 3-button navigation / hardware keys

The callback can be called as follows if it supports the `onBackStarted()` and `onBackCancelled()` methods:
- `onBackStarted()` is called when the back button is pressed (`ACTION_DOWN`) and `keyEvent.getRepeatCount()` is `0`.
- `onBackCancelled()` is called when the back button is released (`ACTION_UP`) and the `keyEvent.isCanceled()` is `true`.
- `onBackInvoked()` is called when the back button is released (`ACTION_UP`) and the `keyEvent.isCanceled()` is `false`.

Test: atest OnBackInvokedCallbackGestureTest
Bug: 278634019
Change-Id: Iba5a27e68607ce33c38dbbc818d66e8753688761