WM: Track focus changes in AccessibilityController

Forward focus changes from input and tracks them
in AccessibilityController. This will help track embedded window
focus changes as well and rely on input as the source of truth
for focus. Accessibility service will start querying the controller
for focus changes.

Bug: b/188792659
Test: presubmit
Test: test talkback
Change-Id: I21a6f1a7353844d2b0f59f32e802ed1f0a3d66ff