Update pretty-printing of signatures in hover messages to mimic the formatting in hovers from the TypeScript language server

[olafurpg]

tsserver includes the name of the symbol and a keyword to denote the syntax kind (const/class/interface/...)

[varungandhi-src]

Do we want this to be 1:1 with the old implementation or should we approximate it? The old implementation used to get this to work by starting with a LanguageService → use getQuickInfoAtPosition → the QuickInfo carries a displayParts field, call ts.displayPartsToString on that.

However, we don't have access to a LanguageService object right now and the lower level API which handles the various cases ts.SymbolDisplay.getSymbolDisplayPartsDocumentationAndSymbolKind is not public. Also, that function itself is over 500 lines long, so copy-pasting it in-tree seems like a bit too much. 😬

So the main options seem to be:

• Create a LanguageService object and use the old way of getting the hover text.
• Code a bunch of simple if checks on the node syntax kind and emit text based on that.

[olafurpg]

Do we want this to be 1:1 with the old implementation or should we approximate it?

I think it's best to approximate. The biggest change we need to make is

• Add the symbol kind in parentheses, example (property)
• Add the symbol name
• Add whatever tokens to make it look like valid syntax, like a const keyword or a : colon in const x: Type