Fix accessibility for connected display status bar icon

Now it has a content description, and every time the green icon animates in "Display connected" is announced.

The icon is now selectable as well.

Fixes: 306525994
Fixes: 306522117
Fixes: 306527238
Test: SystemStatusAnimationSchedulerImplTest
Change-Id: I072daedb3e5873d640ae6da2ea319619a5bb32d1