Expose if running a11y service has crashed

Using a hidden variable to communicate this for enabled
services. Used in Settings to report the current status.

Fixes: 35219990
Test: Adding unit test to verify that crashed value is
populated correctly. Run a11y unit and cts tests.

Change-Id: Ia47a8bd1d750186c504758df21e05a8a76c285cb
7 files changed