Jupterlab source build - how are the content of directory staging/ got populated?

FYI, our release process is largely automated (to build that staging directory to make a package, etc.) The release process is documented at jupyterlab/RELEASE.md at ff1bb771f819d0fdcecc6e5770d453473978625d · jupyterlab/jupyterlab · GitHub, and in particular the step that populates the staging directory is jupyterlab/RELEASE.md at ff1bb771f819d0fdcecc6e5770d453473978625d · jupyterlab/jupyterlab · GitHub