Add "Restore" a11y text to maximize button when it's a restore state.

When the maximize button becomes a restore button/action, we should
change it so a11y services announce that.

Bug: 329351829
Test: Manual. Enable talkback, focus on the button when it's in Restore
- hears "Restore"
Flag: EXEMPT bugfix

Change-Id: I253f96d789abb3c891a23aa64f90025faeefafdd