Auto-Generate All Solution File

[michael-hawker]

We should have a solution template but then auto-generate the required All-up solution to detect/inject the required experiment projects.

This should also let us toggle between running on Uno.UI vs. Uno.WinUI for the platform heads for when we want to test each set all-up, as discussed in #28.

This also simplifies how templating works.

We expect developers to be focused on individual experiment solutions, so not having an all-up solution lends itself to that, and we only need this to build or test the sample locally for more complex development activities.

We'll just have to run the script ahead of time to get it.