VS: Make Fantomas auto-discoverable when user invokes F# format document/selection

We should make Fantomas-for-VS auto-discoverable, e.g. suggest the marketplace addin by the community when the user invokes F# format-document or format-selection

----

Old notes:

I can't format any code in F# with VS2017, using the edit/format/advanced/document or selection. This is working perfectly in VS2015.

In VS2015 I had this issue at some stage and if disabling the the "Productive Power Tools", the edit/format started to work normally.
Then, if enabling the "Productive Power Tools" again, the edit/format functionality keept working and I had no issues anymore. All good in VS2015.

In VS2017 I installed the proper "Productive Power Tools", expecting no issues, but noticed the edit/format was not working. I decided to disable this functionality (in Extension and Updates) as I did for VS 2015 to see whether the issue is solved. But it did not solve the problem.

* Operating system --> MS Windows 10 Pro
* Editing Tools (e.g. Visual Studio Version) --> VS2015 Community Edition