Use ProjInfo for generating project args/options in tests.

[safesparrow]

Plan:

1. Create a dotnet tool that calls ProjInfo, generates fsc args (and optionally FSharpOptions) and saves them in a file
2. Unit tests/other endpoints invoke it via dotnet generator Project.fsproj and read the args

Current state:

• projinfo_for_tests branch contains code
• Instead of a dotnet tool, ArgsGenerator project is inside the codebase
• There is an issue with ProjInfo where it doesn't set the right MSBuild properties and the args it returns do not allow for successful compilation/type-checking - talking to ProjInfo maintainers atm.