- Use appstreamcli to validate appdata

- Add the `<developer><name>` tag

More information: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-developer

This tag is useful to extract keywords and categories

"All graphical applications having a desktop file must have this tag in the MetaInfo. If this is present, appstreamcli compose will pull icons, keywords and categories from the desktop file."

More information: https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/#launchable

Remove .desktop extension from the ID part.

Suggestion: https://gitlab.gnome.org/GNOME/gnome-font-viewer/-/merge_requests/56#note_2029554