Improved expand accessibility experience

The expand action is now on the notification itself
instead of the expand button, this way a user immediately
know if it is expanded.
It also improves the click feedback of the expand button

Test: add notifications, observe accessibility feedback
Change-Id: I9c397d839df52d5354d7ae16725ce3e595da19c7
Fixes: 32322410
Fixes: 35064589