[QSDetailedView] Make details title/sub-title mutable states of string

The title and sub title can change during the UI life cycle. Make them
the `State<String>` instead of `String` in the TileDetailsViewModel.

Applied the business logic to update the title and subtitle for the
internet details view.

Bug: 393448311
Flag: com.android.systemui.qs_tile_detailed_view
Test: InternetDetailsContentManagerTest
Change-Id: Ib88aa866884eb03cdc2f05d18150d399003b8e9b