Rudimentary export goal support for `node_modules`

[tobni]

This is fairly bare bones. I've tested it by exporting the in-repo test projects and then verifying that pycharm auto detects the node_modules produced.

I'm fairly certain the changes to the export goal are benign, but might have made it less flexible for plugin-implementors?

Fixes https://github.com/pantsbuild/pants/issues/19239