Fallback to focused window state if input focus target is not a window

- If the current input focus target is neither a window nor embedded
  window, then accessibility should fall back to using the currently
  focused window for computing changes

Bug: 424253885
Flag: com.android.window.flags.use_input_reported_focus_for_accessibility
Test: atest AccessibilityWindowManagerTest
Change-Id: I2b9185d8a0df164198f6ced67307d96f633e866f