Download JavaScript dependencies at build time

[ebruchez]

See also #3897, which discusses scalajs-bundler.

Based on this article, it seems that scalajs-bundler is no longer the way to go. However, it's not clear what the path forward is, as that article describes interop with vite.js, which we are not using right now.

At least the following modules are currently unmodified and could be included at build time:

• TinyMCE (but see Consider switching to license-friendly text editor #4632)
• CodeMirror

[ebruchez]

Right now, we include JavaScript files directly in our build, and not as modules.

Top-level files, properties describing a JS baseline, and XBL components express dependencies on JavaScript files directly.

webjars could work, and still appears maintained, but it doesn't seems to be "the future". This would allow us to download JAR containing JavaScript files, and then, through some build magic, include the assets into our artifacts.

[ebruchez]

Baby step:

• use npm to download JavaScript assets
• then we somehow access/copy those assets from node_modules