Move the Hover LSP provider to use the new quickinfo service

[333fred]

@david-driscoll this does what it says on the tin. Hopefully this will be another thing that we can get working in vscode. I'm unsure what the Range in LSP represents here, though: is it supposed to be full range of the thing being hovered over? If so, I'm not sure if we actually want to implement that: I'm used to highlighting either getting every instance of a thing, or not highlighting it at all. If we do want to implement that, though, it would be very straightforward to add, as QuickInfo already has the info.

Fixes #1806.

[filipw]

thanks

[david-driscoll]

Thanks @333fred

[bstaletic]

I'm migrating my client to use LSP with OmniSharp-Roslyn.
I would have expected textDocument/hover to provide a docstring and type if available.
That used to be the case with the TypeLookupRequest.
Now, with the QuickInfoRequest, I am only getting the type information.
How are LSP clients supposed to get docstrings?

EDIT:

Ah, just figured it out!
Previously, these comments were considered:

                /// an integer, or something
                private int an_int;

But now the docstring has to be wrapped in <summary>.