Context: https://github.com/dotnet/maui/pull/807
When implementing a new `@(MauiSplashScreen)` feature for .NET MAUI, I
found out that Catalyst doesn't have support for splash screens.
I even tested this in Xcode:
* Create a new Objective-C iOS app
* Make `LaunchScreen.storyboard` red and `Main.storyboard` green.
* Check the new `macOS` checkbox in project settings to enable
Catalyst and be a multiplatform app.
I see red, then green on iOS but only green on macOS. I think Catalyst
completely ignores `UILaunchStoryboardName`.
This removes splash screens from the `dotnet new maccatalyst` template
as well as the `MyCatalystApp` sample project.
Also
* Fix the Mac Catalyst sample to use the correct contents.json and images sizes
for Mac Catalyst app icons.
* Fix the contents.json and image sizes for the Mac Catalyst test project as well.
* Add unit test for Mac Catalyst that ensures that Assets.car is in the final app.
Fixes https://github.com/xamarin/xamarin-macios/issues/10804.
Jonathan Peppers
Rolf Bjarne Kvinge