Make F# installation inside VS folder version agnostic

Currently, the installation of F# specific bits inside Visual Studio are within a version-specific folder.
That folder name is configured in this repo, and has to be maintained. If that is not done, build launched from VS failed.
`\Microsoft\VisualStudio\v17\FSharp\`

The request is to make the installation version agnostic.

This has to be done with care due to projects using the legacy, non-SDK, project system.
There are many project files following this pattern:
https://github.com/MSRCCS/Prajna/blob/b982ed83bdd6e4fafcb6d5b8c75c69a2ffff7a9f/src/ULib/ULib.fsproj#L74
```xml

$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)\FSharp\Microsoft.FSharp.Targets

```

A possible solution might include a version agnostic folder PLUS shortcuts that would meet the needs of legacy projects.