…Roslyn's QuickInfoService

The existing provider uses a custom handler, which this replaces. Among other benefits, this brings nullability display when available, and ensures that any new additions to roslyn's info get propagated to users of this service. Unfortunately, however, TaggedText in VS is significantly more powerful than vscode's hover renderer: that simply uses markdown. Their implementation does not support any extensions to enable C# formatting of code inline, I created a poor-man's substitute: for the description line, we treat the whole line as C#. It does mean there can be a bit of odd formatting with `(parameter)` or similar, but this exactly mirrors what typescript does so I don't think it's a big deal. For other sections, I picked sections that looked ok when formatted as C# code, and I otherwise did a simple conversion, as best I could, from tagged text to inline markdown.

Rewrite quickinfo loop to be fully iterative and not create closures.
Moved the new service to V1.
Simplify the output.

…ing parts that the client needs to reassemble themselves.