Include link to rule documentation in LSP diagnostics

[rchl]

It would be useful to have a link to the documentation of the relevant rule for diagnostics reported when running in LSP mode. For example here we see a diagnostic specifying a rule name but we can't click the rule name to show more information about the rule.

Here is an example of a different diagnostics from eslint with a documentation link:

Per LSP documentation, the Diagnostic object can specify codeDescription property which includes an URL. This can be used for this purpose and this is what eslint uses. For example:

{
  "diagnostics": [
    {
      "code": "space-in-parens",
      "codeDescription": {
        "href": "https://eslint.org/docs/rules/space-in-parens"
      },
      "message": "There should be no space before this paren.",
      "range": {
        "end": {
          "character": 41,
          "line": 1019
        },
        "start": {
          "character": 40,
          "line": 1019
        }
      },
      "severity": 1,
      "source": "eslint"
    }
  ],
  "uri": "...ts"
}

[rchl]

Note that eslint also provides an extra code action for opening the rule documentation link but this does not necessarily belong in the same issue. Also, it's a bit special because it needs custom editor command to trigger opening of the link in the browser.

[ematipico]

@rchl for feature requests, we use GitHub discussions :)

[rchl]

Would it make sense for the new issue template to have Feature request entry that links to discussions? :)