How do you register routes for pages not in the Shell visual hierarchy?

Detail pages that aren't tabs or flyout items must be registered with Routing.RegisterRoute("route", typeof(Page)) in AppShell's constructor. Then GoToAsync("route") can push them. This keeps deep, contextual pages out of the top-level navigation while remaining routable.

public AppShell()
{
    InitializeComponent();
    Routing.RegisterRoute("details", typeof(DetailsPage));
    Routing.RegisterRoute("edit", typeof(EditPage));
}