feat: Provide reference lens data for VSCode

[artempyanykh]

When client's experimental.codeLensFindReferences capability is set (only VSCode plugin now), Marksman will output extra data for the code lens command that can be used to implement client-side behavior to show references when clicking on the lens, e.g.:

"command": {
            "title": "1 reference",
            "command": "marksman.findReferences",
            "arguments": [
                {
                    "uri": "file:///<path>.md",
                    "position": {
                        "line": 62,
                        "character": 0
                    },
                    "locations": [
                        {
                            "uri": "file:///<path>.md",
                            "range": {
                                "start": {
                                    "line": 12,
                                    "character": 2
                                },
                                "end": {
                                    "line": 12,
                                    "character": 19
                                }
                            }
                        }
                    ]
                }
            ]
        }
    },...

where command's arguments are:

1. uri and position is file + pos of the lens,
2. locations is uri + range for each reference.