TVSidebarDetailContainer now exposes a showsDismissButton flag instead of
always attaching a Done toolbar item. The button is only enabled where a
view can end up with no focusable element on its own — Device
Capabilities (informational rows) and the Import Playlists/Subscriptions
flows.
Wrap Contributors, Translators, Acknowledgements, and Device Capabilities
destinations in TVSidebarDetailContainer for the consistent sidebar look,
and make the Translators/Acknowledgements rows focusable on tvOS by
wrapping them in Buttons so the Menu remote button can pop the stack.
On tvOS, ContentUnavailableView inside a Group doesn't expand to fill
available space — it sizes to content and aligns top-leading. Add
.frame(maxWidth: .infinity, maxHeight: .infinity) to all instances
so they center correctly in their parent containers.
