Added documentation that ViewRootImpl#mAccessibilityFocusedVirtualView
may be stale except for bounds and sourceNodeId. And recreate
the node when a11y services calls findFocus.
Checked other usages of mAccessibilityFocusedVirtualView(including
getter method) and verified they are OK.
Fix: b/192706021
Test: tested with Jetpack Compose progress indicator and radio button.
Without Jetpack Compose side workaround, this fix works well with
talkback google3 head.
Change-Id: I40c42011512e3d1fccd1ae8a16a62cbf500cf2ad
be503699e2