AssemblyBuilder.Save in .NET 8

[ShalokShalom]

Prototype: https://github.com/dotnet/runtimelab/tree/feature/assembly-builder-save

Issue: dotnet/runtime#15704 (comment)

Hint: Once this is implemented, change the Readme accordingly

[RyanLamansky]

If this ships I will definitely plug it in 👍

[Terricide]

Looks like it is in .net 9.0 preview

[RyanLamansky]

If it's still there when .NET 9 releases, I'll integrate it!

[RyanLamansky]

.NET 9 seems to have shipped with a way to save assemblies. I haven't tried it yet, but the API looks like what we need.

Some work is required to integrate it. In particular, the compiler assumes that the user will figure out how to supply all the imports and accept the exports, but when saving a DLL, people will expect to have generated types to cover both sides of that. So, the beginning and end of the compilation process will need some updates. I'll work on this when I have time, but PRs are always welcome 😇