Implement labelDetails for CompletionItem

[rgrunber]

This depends on #2348 (LSP >= 3.17)

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#completionItemLabelDetails

When returning a list completion items, we set the label to contain a lot of information :

{
  "label": "getLogger(String arg0, ResourceBundle arg1) : Logger",
  "kind": 2,
  "detail": "System.getLogger(String arg0, ResourceBundle arg1) : Logger" 
...
...

It looks like the type signature information, as well as fully qualified names / file paths could be rendered more elegantly if we use this new property.