Update desktop app header a11y strings so buttons announce app name

Close Window, Minimize Window & Maximize/Restore Window buttons will now
announce "Close/Minimize/Maximize/Restore (App Name), double tap to
close/minimize/maximize/restore app window"  when focused by talkback
a11y focus

Fix: 397578815
Test: Enter deskop windowing with an app, turn on Talkback, select app
header buttons and listen for talkback announcement
Flag: EXEMPT bugfix

Change-Id: I00c735637777e871c366aeabfa03c5f52f10553d