- Use the `<developer><name>` tag instead of the deprecated `<developer_name>`
- Implement appstreamcli for extra appdata validation
- Fix a release description
- Update the donation URL
- Add the translation tag
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3071>
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