Reuse settings in contributes.configuration section of extension's package.json

[mcsknp]

When define available configurations for extension in contributes.configuration section of package.json, I can't reuse some properties for other like definitions in JSON schema.
As below:

{
    // ...
    "contributes": {
        // ...
        "configuration": {
            "definitions": {
                "something": {
                    // ...
                }
            },
            "someconfig": {
                "$ref": "#/definitions/something" // or anyway to reference to above definitions
            }
            // ...
        }
        // ...
    }
    // ...
}

[aeschli]

The configuration extension point only supports a subset of JSON schema: See https://code.visualstudio.com/api/references/contribution-points#Configuration-property-schema.

$ref is not part of it.

I made it more explicit with microsoft/vscode-docs@7108f81

We can allow the use of refs when we support when we support "$id" references. #92042

duplicate of #81782