Support JSON property name

[inouetakuya]

I think it would be easier to see the JSON property names and values in a different color, as in the JetBrains IDE.

VSCode Darcula theme

JetBrains IDE（RubyMine）

[inouetakuya]

The color of JSON property names can be changed by setting the following in Settings.json.

{
    "editor.tokenColorCustomizations": {
        "[Darcula]": {
            "textMateRules": [
                {
                    "name": "JSON Property Name",
                    "scope": "support.type.property-name.json",
                    "settings": {
                        "foreground": "#9876AA"
                    }
                }
            ]
        }
    }
}

After