Dev15.6 -- Fix multi-targetting / F# IDE

[KevinRansom]

Multi-targeting doesn't work correctly in the F# IDE.

Relies on this Project System PR: dotnet/project-system#3198

The reason is the IDE doesn't know how to identify the correct cached references and source files. Currently it uses the project file name, this is insufficient because in a multi-targeting project there is in fact an in memory project for each target framework.
The project tracker can identify the correct in memory project using the binpath of the project output file. In the project system the context object also identifies the binpath for the project being "design-time" built.

This change modifies the CommandLine notification to send the binpath rather than the project path.

The code can handle the existing behavior of the CommandLine If the binpath doesn't find a project, it then tries the project file name. And behaves the same as before.

Kevin

[brettfo]

pending ship room approval

[cartermp]

Link #4084 - I suspect that this will be difficult for OSS folks to test.

@ctaggart and @eiriktsarpalis, can you help provide some examples of things you'd like to do so that we can test those scenarios prior to merging?

[ctaggart]

Here is an open source one I just created. I can't set a breakpoint in Froto.Parser if I make it multi-targeting. Try running Froto.Compiler and setting a breakpoint anywhere in Froto.Parser.

git clone -b TargetFrameworks https://github.com/ctaggart/froto.git
dotnet restore .\Froto.sln
.\Froto.sln

[KevinRansom]

@ctaggart
With Fixes:

Shipped version:

[eiriktsarpalis]

I think fixing intellisense and debugging are the main blockers for me.

Another issue is that net4x projects using the new project structure lose the ability to do certain useful things such as "Send references to F# Interactive" or "Send Project output to F# Interactive". Would be nice to get this back eventually.