A new package.json stanza for replacing plugins (jupyterlab.replacePlugins?)

[krassowski]

Problem

Native JupyterLab plugins can be disabled by extensions using jupyterlab.disabledExtensions key in package.json . However, if an extension is composed of multiple plugins and a plugin X (which replaces the native plugin Y) gets disabled there is not easy way to re-enable the native plugin Y (an extension author must then create another plugin Z which checks if X is disabled and if it is then replicate the behaviour of native Y).

Proposed Solution

We could have allow objects within disabledExtensions:

{
  "jupyterlab": {
     "disabledExtensions": [
        // short form
        "@org/core-extension:plugin-a",
        // proposed long form
        {"disable": "@org/core-extension:plugin-b", "ifEnabled": "@org/external-extension:plugin-a"}
    ]
  }
}

or we could add a new dedicated stanza:

{
  "jupyterlab": {
     "replacesPlugins": {
        "@org/core-extension:plugin-b": "@org/external-extension:plugin-a"
      }
  }
}

Additional context

This affected jupyterlab-lsp as reported in #15649