Make testing of feature compiler branches more accessible

[Szer]

I would like to start a discussion around making preview (nightly?) version of compiler with "bleeding-edge" features still not merged in master more accessible.

Currently bleeding-edge testing is available primarily for active collaborators of dotnet/fsharp because consuming of custom compiler version requires knowledge of build and publishing process as well as knowledge of how to hijack your MSBuild to give it custom FSC.exe

Features like
https://github.com/dotnet/fsharp/tree/feature/nullness
https://github.com/dotnet/fsharp/tree/feature/tasks
https://github.com/dotnet/fsharp/tree/feature/erased-unions
and many others could benefit greatly from those brave community members who are willing to experiment with them but currently out of the loop of dotnet/fsharp publishing process.

I'm personally never touched compiler publishing process and doesn't know how to plugin custom version in my MSBuild but feeling myself brave enough to test these awesome features on daily basis.

How it could be done?

• Create a short guide how to plugin custom compiler artifact
• Create another guide how to produce such artifact from random branch (I couldn't find anything related here)
• Create an automated process which will create such artifacts from all feature/* branches ready to consume
• Anything else which will make testing of feature compiler branches more accessible