feat(anywidget): expose model.widget_manager

[manzt]

Fixes #193. This can be useful for creating container widgets and avoids exposing more backbone/jupyter-widgets internals.

import anywidget
import ipywidgets as ipw
import traitlets

class Box(anywidget.AnyWidget):
    _esm = """
    async function unpack_models(model_ids, manager) {
        return Promise.all(
            model_ids.map(id => manager.get_model(id.slice("IPY_MODEL_".length)))
        );
    }
    export async function render({ model, el }) {
       let model_ids = model.get("children");
        let children_models = await unpack_models(model_ids, model.widget_manager);
        for (let model of children_models) {
            let child_view = await model.widget_manager.create_view(model);
            el.appendChild(child_view.el);
        }
    }
    """
    children = traitlets.List(trait=traitlets.Instance(ipw.DOMWidget)).tag(sync=True, **ipw.widget_serialization)

Box(children=[ipw.IntProgress(), ipw.IntSlider()])

[netlify]

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[codecov]

Codecov Report

Merging #194 (b48db57) into main (fa84359) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #194   +/-   ##
=======================================
  Coverage   98.11%   98.11%           
=======================================
  Files           8        8           
  Lines         424      424           
=======================================
  Hits          416      416           
  Misses          8        8           

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