Add CLI to fetch pyodide release

[rth]

Sometimes we have to do from time to time is to fetch and extract a given pyodide release (e.g. here). It would be nice to have a CLI command to do that. Maybe something like,

pyodide fetch-release --tag 0.21.0 <output-path (defaults to .)>  

Possibly related to CLI / venv tools by @hoodmane in pyodide/pyodide#2976

[rth]

@ryanking13 made a similar proposal earlier in pyodide/pyodide#2402

From the discussion (pyodide/pyodide#2394 (comment)), it would be good to provide an official way to download Pyodide packages into the local filesystem for Node users, so that they don't need to manually download it from e.g. Github release.

Example: pyodide install (npx pyodide install)

For a reference, other npm packages that need to download external binaries do:

puppeteer: has a install script which downloads Chromium browser binary when doing npm install puppeteer.

playwright: has a command playwright install to download browser binaries (and ffmpeg).

Though I think "install" is too general a name in our case, as there are a lot of things we install (in a venv, cross-env, build dependencies etc)

[ryanking13]

Thanks for opening an issue! Indeed it would be great to have something like pyodide fetch-release.

I think the proposal in pyodide/pyodide#2402 still valid BTW. I think we can add a initialize script in our JS package so when npm install pyodide is executed, we can make wheels are downloaded automatically into the node_modules/pyodide.