The newly added developer name syntax appears not implemented
across related platforms: GNOME Software, Flathub, etc.
There is no harm in using both deprecated and newly introduced
tags together, and neither appstream-glib nor appstreamcli
fails to validate this usage.
- Add appstreamcli support to validate the appdata file.
- Add missing release information.
- Use the `<developer><name>` tag instead of the deprecated `<developer_name>`