Two Islands Example

Could be useful to have an example of showing how to use Two different Islands.

For instance maybe there's a `TabbedCommandBar` or `TabView` as the top-level navigation, but then a `DataGrid` is used as the main page's content.

Start by reviewing the existing sample structure for how Windows Community Toolkit controls are demonstrated in the C++/WinRT UWP application. Add a Two Islands example using a TabbedCommandBar or TabView for top-level navigation and a DataGrid for the main page content; done means the sample clearly shows both controls working together.

Written by the indexing model from the issue text.