Let's move the nautilus plug-in into nautilus git repo
I think core GNOME modules should not be shipping with a nautilus plug-in, because it's not included in the Nightly flatpak of Files and, as a result:
- The application as developed and tested by its maintainers looks and behaves differently from the application as released by the release team.
- The application CI pipeline is not going to warn us if we break core plug-ins on any MR. We already have a few in-tree plug-ins which originated in other modules.
Doing this earlier would have prevented the unexpected breakage in 43.alpha. But it's still useful to do it now, because more API breaks are coming.