How to use Icons in `package.json` for Language Icon

[dschiller]

Describe the bug
In package.json one can use icons like

...
            "commands": [
            {
                "category": "Testplan Manager",
                "command": "testplanManager.document.goTo",
                "title": "Go to",
                "icon": "$(arrow-right)"
            },
...

But that doesn't work for languages:

...
    "contributes": {
        "languages": [
            {
                "id": "testplan",
                "aliases": [ "Testplan" ],
                "extensions": [ ".tp" ],
                "configuration": "./language-configuration.json",
                "icon": {
                    "dark": "$(arrow-right)",
                    "light": "$(arrow-right)"
                }
            }
        ],
...

Because there it seems we need to use SVG files. As you provide the SVG Sprite option:

<svg>
    <use xlink:href="codicon.svg#add" />
</svg>

How to use this approach or another in package.json for language icons ?

To Reproduce
Steps to reproduce the behavior:
See description

Expected behavior
See description

Screenshots
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Environment

• OS: Mac
• VS Code Version:
  Version: 1.97.2 (Universal)
  Commit: e54c774e0add60467559eb0d1e229c6452cf8447
  Date: 2025-02-12T23:20:35.343Z (2 wks ago)
  Electron: 32.2.7
  ElectronBuildId: 10982180
  Chromium: 128.0.6613.186
  Node.js: 20.18.1
  V8: 12.8.374.38-electron.0
  OS: Darwin arm64 23.6.0

Additional context
Add any other context about the problem here.

[dschiller]

Seems my question 2.5 half years ago didn't get any attraction at https://stackoverflow.com/questions/74125516/how-to-use-built-in-icons-for-language-contributions-in-a-vscode-extension