feat: adding IApplicationBuilder

[dansiegel]

GitHub Issue (If applicable): #

• Simplify App Bootstrapping #918

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

All code revolves around the IHostBuilder

What is the new behavior?

A new IApplicationBuilder has been introduced to help simplify the process of bootstrapping the application startup. Currently the ShowAsync has been moved to the template until we determine the best location for this as Toolkit Navigation doesn't actually have a reference to Hosting so it cannot access IApplicationBuilder. There is also no current way to pass the boolean for Uno logging when creating the Host.

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)

Other information

Internal Issue (If applicable):

[nickrandolph]

Looking good but a couple of outstanding things:

• Need to update Logging to provide implementation of IServiceInitialize for when unologging is enabled
• Need to alter InitializeNavigationAsync so that there's only one method and that if user calls UseToolkitNavigation, Navigation.Toolkit gets an opportunity to initialize either LoadingView or SplashScreen accordingly

[welcome]

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