[themes] Allow textmate token color customizations to reference existing scope

[0xc0]

Allow the ability to reference an existing token

Use case

Instead of needing to have

  "editor.tokenColorCustomizations": {
    "[Default Dark+]": {
      "textMateRules": [
        {
          "scope": "markup.italic",
          "settings": {
            "foreground": "#dcdcaa"
          }
        }
      ]
    },
    "[Default Light+]": {
      "textMateRules": [
        {
          "scope": "markup.italic",
          "settings": {
            "foreground": "#795e26"
          }
        }
      ]
    }
  }

in which the foreground color is copied from the support.function foreground color of each theme and repeating for each theme, something similar to the following:

  "editor.tokenColorCustomizations": {
    "textMateRules": [
      {
        "scope": "markup.italic",
        "settings": {
          "foreground": {
            "referenceScope": "support.function",
            "referenceSetting": "foreground"
          }
        }
      }
    ]
  }

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• [theming] set foreground of 'Open Changes', 'Replace' and 'Replace All' icons (#33346)

[ghaschel]

This would be really useful