Use input-reported focus for accessibility

- Input is the source of truth for window focus, which is currently
  partially propagated to Accessibility, we need to migrate the
  remaining focus logic to use the input-provided state to ensure
  the embedded windows (which are increasingly used in SysUI) can
  be correctly focused when shown.
- In particular we need to update the WindowInfo.focused state
  consistently for both WindowStates and embedded windows, to
  populate it based on the last reported focused window token,
  which also allows us to remove the duplicate isFocused state in
  AccessibilityWindow itself

Bug: 378565144
Flag: com.android.window.flags.use_input_reported_focus_for_accessibility
Test: atest AccessibilityWindowManagerTest
Change-Id: I2e77b13a0007907e3ba67e779cf759f254ef8191