Switch to use anywidget

[marthacryan]

Co-authored by @manzt! This updates the logic for the FigureWidget to rely on anywidget.
A quote about anywidget from the documentation for context:

anywidget is both a specification and toolset for authoring reusable web-based widgets for interactive computing environments. As a specification, it defines a standard for widget front-end code. As a toolkit, it provides tools for authoring widget front-end code according to the specification, as well as a Python library that simplifies creating and publishing custom Jupyter Widgets.

This will not affect the go.Figure class. High level explanation of the difference between using go.Figure and go.FigureWidget:

• go.Figure: The chart generated by this object will be interactive on the client side. For many purposes, this is all a user needs to do with a chart. The interactions are things like zooming in, or any of the various operations in the toolbar.
• go.FigureWidget: The difference here is that the figure is interactive on the server side as well.
  • Interactions with the plotly chart can be sent to the python kernel and used in other widgets.
  • Interactions with other widgets can be used to control the chart

[manzt]

sourcemaps will make it easier to debug when developing the widget using the browser developer tools.

[manzt]

I added the --minify and --alias flags. minify makes the final bundle smaller.

The alias here is to make the import nicer for typescript type checking types (tsc), while esbuild needs to point to the actual files (./dist).