Using ipywidgets with standalone cell view/output

[krassowski]

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Problem

It's currently hard to use ipywidgets outside of existing notebook and console widgets. It should not be.

Proposed Solution

Expose registerWidgetHandler? Generalize it to take Notebook | Console | IDisposable argument?

https://github.com/jupyter-widgets/ipywidgets/blob/b24fa6be5a289a23dd82eedcecbf6603ddbe2c0a/python/jupyterlab_widgets/src/plugin.ts#L168-L174

Additional context

Related to https://github.com/jupyterlab/jupyterlab/issues/16227