Overall rework of the PKGBUILD
Context: https://archlinux.org/todo/general-xfce-packages-rework/
- Update URL (point to upstream doc webpage for the package)
- Use SPDX identifier for the license
- Switch to a more transparent source (auto-generated GitLab archive)
- Add check()
- Add nvchecker integration (.nvchecker.toml)
This MR acts as a rework proposition for the rest of the packages. If we agree on these changes, I'll proceed to apply them to every XFCE packages.