Use coincident if crossOriginIsolated, comlink otherwise

[jtpio]

Similar to jupyterlite/pyodide-kernel#126

Refactor the code to align the implementation on https://github.com/jupyterlite/pyodide-kernel, so it's easier to switch between the code bases and find the same patterns.

Fixes #102

[jtpio]

Looks like the use of postMessage in xeus-lite may need some investigation: https://github.com/jupyter-xeus/xeus-lite/blob/b1c9e1fd29caa88e7ebb2dd06c798c248ed01b0c/src/xserver_emscripten.cpp#L24-L32

[martinRenou]

@jtpio this should be ready now. Would you be able to have another look?

[martinRenou]

@jtpio thanks for your review! I added the comment as you suggested, will go ahead and make a release with this

[jtpio]

It would also have been nice to mention this change in the changelog for visibility: https://jupyterlite-xeus.readthedocs.io/en/latest/changelog.html

For the docs, there is already some content https://jupyterlite.readthedocs.io/en/stable/howto/content/python.html we could link to.