Add a Panel native widget

[MarcSkovMadsen]

Mosaic works with Panel via the ipywidgets-bokeh integration. See https://discourse.holoviz.org/t/panel-works-with-anywidget/6466/3?u=marc.

The ipywidgets-bokeh integration is not as performant as a Panel native implementation. With Panel 1.5 it should in theory require no change on the js side and only minor changes (traitlets -> param) on the python side to create a Panel native widget. See https://panel.holoviz.org/reference/custom_components/AnyWidgetComponent.html.

Please consider adding a Panel Mosaic widget. It could be in a separate module from mosaic_widget.panel import MosaicWidget.

I've made a similar request in the Panel github to add it there instead. I've included some code that should illustrate a POC in holoviz/panel#7358 (comment). Unfortunately some error is raised in quantitative.js. I'm not a js developer so figuring out what goes wrong is not easy for me.

[domoritz]

Thanks for the motivation and outline of a solution. I think this would be great and could live in this repo. I won't have cycles to do this for a while but would be happy to review a pull request.