Punt to Javascript for text encoding/decoding

[mdboom]

The tables for some of the larger CJK encodings are quite large in the Python implementation. There should be no need for this, since the browser / OS already has them.

We should punt out to Javascript to handle encoding/decoding for codecs that we don't ship with Pyodide -- requiring some mapping between the Python names for the codecs and the web ones.

There is a polyfill here to handle some of the cross-browser differences.

I'd consider this very low priority. Python code should generally stick to Unicode and let the input/output layer handle encoding/decoding anyway.

[hoodmane]

@rth @dalcde Since pr #79 supposedly obsoletes this, seems like it could be closed.

[rth]

Thanks @hoodmane ! Closing as resolved by #79