Error details were declared in the video info view and the expanded
player, and Open Link three times: at the app root for deep links and
for the File menu command, and on Home. All of them are now AppSheets;
the deep link and menu requests go through the global request, so a
deep link that arrives while the player is expanded no longer opens the
sheet behind it.
The four sign-in modals that were a full-screen cover on tvOS and a
sheet elsewhere, each written out twice, use a platformSheet helper.
