Implement tooltips for keywords

[dsyme]

Hovering over F# keywords in Visual Studio and VS Code does not give a tooltip.

This is one of our best ways to help educate newcomers about the correct use of the F# language, e.g. both with a good tooltip and also aka.ms links to good articles in the .NET documentation (e.g. the main article on pattern matching for the match keyword)

Some basic information about keywords is already available in KeywordsWithDescription but we can give more information that this

[baronfel]

We do support keyword tooltips in FSAC/Ionide:

We take the list of keywords and descriptions to power this, so any enhancements here will seamlessly flow down. I'm all for it!

[dsyme]

OK thanks, yes I didn't get that when I tried in Ionide but I think the project context wasn't loaded correctly

[dsyme]

@vzarytovskii @KathleenDollard Reviewing things, this seems like really low hanging fruit for improving VS