Touch exploration separate setting and API to poll the latter state.

1. Seperated touch exploration to be a seperate setting rather being
   magically enabled by the system of accessiiblity is on the there
   is at leas one accessibility service that speaks enabled. Now
   there is a setting for requesting touch exploration but still the
   system will enabled it only if that makes sense i.e. accessibility
   is on and one accessibility service that speaks is enabled.

2. Added public API for checking of touch exploration is enabled.

3. Added description attribute in accessibility service declaration
   which will be shown to the user before enabling the service.

4. Added API for quick cloning of AccessibilityNodeInfo.

5. Added clone functionality to SparseArray, SparseIntArray, and
   SparseBooleanArray.

bug:5034010
bug:5033928

Change-Id: Ia442edbe55c20309244061cd9d24e0545c01b54f