LSP endpoint to provide FSI data to load project references + optional subset of files to load

I'm trying to replicate [the "send references for FSI" feature of Ionide-VSCode](https://github.com/ionide/ionide-vscode-fsharp/blob/d3e65078316dc5d271ccdfbbb42b6b8fca2c68aa/src/Components/Fsi.fs#L158-L167) in [Ionide-vim](https://github.com/ionide/Ionide-vim), but it seems impossible to be done with VimScript since it has not only to parse the `.fsproj` but also to get the actual assembliy locations.

If FSAC can provide an endpoint for getting referenced assemblies, it will make it very easy to implement.