Unable to access ipympl from JupyterLab due to Error displaying widget: model not found

まだ誰も着手していません。

## Describe the issue

I am running an example code to access ipympl from Jupyter Lab on GCP/Linux.

```
%matplotlib widget
import matplotlib.pyplot as plt
import numpy as np
import sys
"ipympl" in sys.modules
True

# Testing matplotlib interactions with a simple plot
fig = plt.figure()
plt.plot(np.sin(np.linspace(0, 20, 100)));

Error displaying widget: model not found

```

## Versions

```
Paste the command output here.

3.8.10 (default, Mar 13 2023, 10:26:41)
[GCC 9.4.0]
ipympl version: 0.9.3
Selected Jupyter core packages...
IPython : 8.12.0
ipykernel : 6.13.0
ipywidgets : 8.0.6
jupyter_client : 8.2.0
jupyter_core : 5.3.0
jupyter_server : 2.5.0
jupyterlab : 3.6.3
nbclient : 0.7.4
nbconvert : 7.3.1
nbformat : 5.8.0
notebook : 6.5.4
qtconsole : not installed
traitlets : 5.9.0
Known nbextensions:
config dir: /usr/local/etc/jupyter/nbconfig
notebook section
jupyter-matplotlib/extension enabled
- Validating: OK
jupyter_resource_usage/main enabled
- Validating: OK
nbdime/index enabled
- Validating: OK
jupyter-js-widgets/extension enabled
- Validating: OK
tree section
jupyter_server_proxy/tree enabled
- Validating: OK
JupyterLab v3.6.3
/usr/local/share/jupyter/labextensions
jupyterlab_pygments v0.2.2 enabled OK (python, jupyterlab_pygments)
dask-labextension v6.1.0 enabled OK (python, dask_labextension)
nbdime-jupyterlab v2.2.0 enabled OK
jupyter-matplotlib v0.11.3 enabled OK
jupyterlab-nvdashboard v0.8.0 enabled OK (python, jupyterlab_nvdashboard)
@jupyterlab/git v0.41.0 enabled OK (python, jupyterlab-git)
@jupyter-widgets/jupyterlab-manager v5.0.7 enabled OK (python, jupyterlab_widgets)
@jupyterhub/jupyter-server-proxy v4.0.0 enabled OK
@jupyter-server/resource-usage v0.7.2 enabled OK (python, jupyter-resource-usage)
@jupyter-lsp/jupyterlab-lsp v4.1.0 enabled OK (python, jupyterlab-lsp)
@elyra/code-snippet-extension v3.15.0 enabled OK
@elyra/script-debugger-extension v3.15.0 enabled OK
@elyra/python-editor-extension v3.15.0 enabled OK
@elyra/metadata-extension v3.15.0 enabled OK
@elyra/pipeline-editor-extension v3.15.0 enabled OK
@elyra/code-viewer-extension v3.15.0 enabled OK
@elyra/theme-extension v3.15.0 enabled OK
@elyra/r-editor-extension v3.15.0 enabled OK
@elyra/scala-editor-extension v3.15.0 enabled OK

Other labextensions (built into JupyterLab)
app dir: /usr/local/share/jupyter/lab

Disabled extensions:
@jupyterlab/launcher-extension (all plugins)
```

JupyterLab 3.6.3 で、`%matplotlib widget` から始まる報告された例を、記載されている ipympl、ipywidgets、および Jupyter パッケージのバージョンを使用して再現します。まず、JupyterLab のウィジェット統合と、有効になっている `jupyter-matplotlib` および `@jupyter-widgets/jupyterlab-manager` 拡張機能を確認します。サインプロットが “model not found” エラーなしでインタラクティブウィジェットとして描画されれば完了です。

索引モデルが issue の本文から書いたものです。