Accessibility services cannot obtain the source of an event coming from a root...

Accessibility services cannot obtain the source of an event coming from a root namespace descendant.

1. The user can touch the screen at an arbitrary location potentially crossing the root namespace
   bounday which will send an accessibility event to accessibility services and they should be able
   to obtain the event source. Also accessibility ids are guaranteed to be unique in the window.
   Added a package scoped findViewByAccessibilityId method that dives into nested root namespaces.

2. Added accessibility support to the AnalogClock.

bug:5405934

Change-Id: I84edcb554bae41aafcbbc2723c5e62c1ef8a6ddf