Consider prototyping VS FSI as a VS command shell window

VSFSI --- is not particularly great.

It is a very simple full screen line editor. That sends lines to an fsi session, and gets sent back text responses. Any improvements that are made to the command line fsi session for example colouring, or the often requested intelli-sense would not surface in the VS implementation.

Visual Studio already has a mechanism for hosting command line applications in a window, we should consider at least prototyping using this mechanism.

Once we have it in place we could perhaps try out using dotnet-repl in place of dotnet fsi