The Extensions app code is now independent enough from the rest of the code
base to move it to its own subprojects, like we did for the extensions-tool.
This allows for stand-alone builds of the app, which we are about to use
for distributing it as flatpak.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1133
I misremembered that imports.package.start() would set up the correct
gettext domain, but the module only provides a convenience method
for doing that.
Use it to bring back translations in the Extensions app, whoops.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1108
