Add FSharp.Build support for reference assemblies

[vzarytovskii]

Add or modify FSharp.Build tasks that will determine if projects need to be re-built or not depending on if the reference assembly output has changed.

See Roslyn's implementation of this: dotnet/roslyn@315c2e1/src/Compilers/Core/MSBuildTask/CopyRefAssembly.cs

[kerams]

Any chance of this making it into .NET 7?

[vzarytovskii]

I believe it's already there, probably has issues though, since we didn't do a comprehensive testing.

[NinoFloris]

Seems like RC2 will contain the enabling bits dotnet/sdk#26306

[vzarytovskii]

Seems like RC2 will contain the enabling bits dotnet/sdk#26306

This is SDK support, FSharp.Build support went in earlier:
#13567
#13263

[NinoFloris]

Right, I was looking for the sdk support because that's what I've been waiting for. @kerams and I are probably commenting on the wrong issue ;)

[charlesroddie]

In VS 17.3.2 I find that reference assemblies seem to work between F# projects, but not F# -> C#. Is it that the feature isn't in released VS yet or is this a bug that I should post about separately?