Pyodide 0.22.0 release

Pyodide 0.22 is a major release focused on improving the foreign function
interface between Python and JavaScript. We also improved the systems for
building, loading, and testing packages. In particular, we added support for
creating virtual environments that execute code using Pyodide in Node.js.

We unvendored the Pyodide package manager and matplotlib backend into separate
repositories. We also added a new command line interface for common tasks
involved in building and testing packages with Pyodide.