[QSDetailedView] Polish cast details view Ui

- add padding for the disconnect button
- add strings to the xml

Bug: 378513588
Flag: com.android.systemui.qs_tile_detailed_view
Test: Only ui polish. Existing unit tests still pass.
Change-Id: Ifa553263c6c84f1b75424a4e67e1ac5d051eeb30