Update the public APIs for finding views by text to optionally use content description.

1. Added flags to the search method to specify whether to match text or
   content description or both.

2. Added test case for the seach by content description.

3. Updated the code in AccessibilityManager service to reflect the latest
   changes there so test automation service works - this is the fake
   service used for UI automation.

Change-Id: I14a6779a920ff0430e78947ea5aaf876c2e66076