[Enhancement] Offer WPF as an option for the Windows host (especially Blazor Hybrid)

## Summary
MAUI is going to use WinUI 3 as its Windows host. WinUI is not something that many .NET developers are going to find very comfortable, so I think offering WPF as a possible host for Windows might cause them less frustration and failure than a WinUI host will.

## API Changes

As I have suggested in https://github.com/dotnet/maui/issues/1557 I think WinUI is outside of the sphere of experience of a lot of .NET developers, and it seems to have some unfortunate side effects on build performance, publishing, runtime dependencies and so on. This is a lot of friction for developers to suffer when they are new to MAUI. I think MAUI is really promising, and I am concerned that a lot of developers will be put off from using it if they have bad experiences with it, even when those issues are not to do with MAUI directly. This could unduly give MAUI a bad name, and that would be a terrible shame.

Is there a way that a WPF host can be made available as an option to replace WinUI? This would be especially beneficial for people who intend to develop their UIs using Blazor, and therefore don't benefit from any of the more modern UI features available in WinUI.

Review the existing WinUI 3 Windows host architecture and the discussion linked from issue #1557, focusing on how a WPF host could fit MAUI and Blazor Hybrid. This issue does not name files or tests; done would require an agreed scope and design for offering WPF as an alternative Windows host.

Written by the indexing model from the issue text.