Announce device name in the add/remove group button content descriptions

Improves accessibility by using the specific device name we're adding
rather than all buttons using the same generic text.

Bug: 421058541
Fixes: 421058541
Test: atest MediaOutputAdapterTest
Test: atest OutputSwitcherTest
Flag: EXEMPT bugfix
Change-Id: Iea9e3c2241279a2f6c51e105b9c29f9cfed9468f