feat: add generic support for displaying Shell

[dansiegel]

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

Due to the overloaded extension in Toolkit Navigation you must provide special logic to handle when the Navigation Root is a Loading View and you must provide your own implementation to handle the ShowAsync for your Shell.

When providing initialNavigate it is ignored and not passed into InternalInitializeNavigationAsync

What is the new behavior?

IApplicationBuilder has a new property Dictionary<object, object> Properties to maintain state when needed between extensions. A new extension is available to use Toolkit Navigation using the IApplicationBuilder. An extension has been added to the core Navigation library ShowAsync<TShell>.
The overload for Window.InitializeNavigationAsync in Toolkit Navigation is now obsolete and will cause an error if used with a message to use the IApplicationBuilder.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Wasm UI Tests are not showing unexpected any differences. Validate PR Screenshots Compare Test Run results.
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)