Set rangeHoverProvider under experimental capabilities

[ayoub-benali]

A workaround for microsoft/language-server-protocol#377 until it is resolved
this would allow LSP clients to explicitly know that they can send a range with textDocument/hover instead of a position

If someone has a better name for the field I am happy to change it :)

@ckipp01 should this be added to new-editor.md ?

[ckipp01]

Cool, seems to do the trick 👍🏼

[Trace - 03:08:12 PM] Sending response 'initialize - (1)'. Processing request took 1445ms
Result: {
  "capabilities": {
    ...
    "experimental": {
      "rangeHoverProvider": true
    }
  },
  "serverInfo": {
    "name": "Metals",
    "version": "0.10.10-SNAPSHOT"
  }
}

As for the name, I think this is fine. Thanks for tackling this! I'll leave this open for a bit in case the others have any comments on it, but if not LGTM!

[ckipp01]

@ckipp01 should this be added to new-editor.md ?

No I think we're good. Under hover we already mention this:

https://scalameta.org/metals/docs/integrations/new-editor/#textdocumenthover