[FEATURE] Remove the non-supported platforms from the runtimes folder

[mattleibow]

When doing a dotnet publish on a .NET Core app (for example a console app), the output folder will have all the supported platforms in the output.

For now, it is a bit annoying, but once #1296 lands, it will literally have all the platforms there. So, when publishing an ASP.NET Core website, it will have the libSkiaSharp.framework there too. It is a nice thought that we can all can run our websites from our iPhones, but not realistic. The games will be glitchy when the world hits our local blog... anyways. 😆

Since I control the NuGet package... I can actually investigate removing the unsupported platforms. I already do this in part for Tizen (which is .NET Core). When publishing a netcoreapp3.0, I can skip all the runtimes for mobile.

What are your thoughts and reasons around this type of inclusion/exclusion of the native runtimes? What are you doing now? What do you want the NuGets to just do for you?

[mattleibow]

Thinking about this some more and I think it might be nice to split the native assets into separate packages now that all the bits are .targets-based. And, this will allow for improved/reduced .targets files.

One of the issue is that Tizen uses the "linux-armel" runtimes folder, which is a valid item for other things. Splitting this into a separate Tizen package that only installs on Tizen means no scripts needed at all.

But, not just that, my previous decision to include the .framework and .so files for iOS and Android in the runtimes folder is a bit premature. This is only going to be useful for .NET 6 and that is a year away.

I want to get at least a stable version of v2.80 out next week (if all is well), so this will have to wait for v2.80.1 - which will hopefully be soon after.