Added new API for URI permissions management.

The new methods are:

- getGrantedUriPermissions(String packageName)
- clearGrantedUriPermissions(String packageName)

These methods will be used by the Settings app to allow users to clear
the URI permissions granted to an application.

BUG: 26447975

Change-Id: I6867402e42b3d6fd03050ec57b73973ccd8a17af