Migrate notification shade to use the a11y panes

The new pane API is intended to manage things that
look like windows but aren't formal windows. The
notification shade and quick settings are a great
example of this. I've replaced explicit requests
for announcements with code that just keeps the
pane title up to date. The correct events are then
dispatched automatically.

Bug: 62231686
Test: I've verified that the correct events are
dispatched using the TestBack experimental
accessibility service. I've also run TalkBack with
the events. TalkBack has an issue with the new API
(b/73126910), so it will be slightly too verbose
until they check the change type.

Change-Id: I8ba130e20b09c69fff65c59af9f08aa6abd2b016