[outline] Use the `DocumentSymbol.detail` not just only the `DocumentSymbol.name`

[kittaakos]

Currently, detail is ignored. It would be nice to decorate the Outline with the detail. Just like Eclipse does with the type information.

[kittaakos]

I have added the bare minimum support for the detail here. No decorations, no fancy colors, just the concatenation of the symbol.label + symbol.detail.

[vrubezhny]

Here's how it's looking with what I have done in PR