Fix TabView selection (#3988)

- Previously, the TabViewListView's SelectedItem was set to the item container. Instead, this should be set to the list item type itself, as that's what is also the ItemsSource of the TabViewListView.

dev/TabView/TabView.cpp

@@ -983,20 +983,7 @@ void TabView::UpdateSelectedItem()
 {
     if (auto&& listView = m_listView.get())
     {
-        auto tvi = SelectedItem().try_as<winrt::TabViewItem>();
-        if (!tvi)
-        {
-            tvi = ContainerFromItem(SelectedItem()).try_as<winrt::TabViewItem>();
-        }
-
-        if (tvi)
-        {
-            listView.SelectedItem(tvi);
-
-            // Setting ListView.SelectedItem will not work here in all cases.
-            // The reason why that doesn't work but this does is unknown.
-            tvi.IsSelected(true);
-        }
+        listView.SelectedItem(SelectedItem());
     }
 }