Add new callback / intent type to ContextHub APIs

Updates the ContextHub APIs to support notifying clients (either through
traditional callbacks or via PendingIntent) that their ability to
communicate with nanoapps has changed.

Also, adds the ability for clients to discover the permissions required
to communicate with nanoapps so they know whether their initial or
subsequent nanoapp messages will successfully be delivered.

Bug: 166846988
Test: compile
Change-Id: I37e475a1457a031890693d2858b5d5f7de34de26