We can't conditionally include the flatpak patch as the flatpak macro
isn't defined when building the srpm in koji, which means that the patch
doesn't get included in the srpm and the flatpak build fails due to not
finding the patch file.
As a fix, change it so that the flatpak patch is always included in the
srpm, but only conditionally applied when building for flatpak.
While at this, also guard gschema.xml %files entry with 0%{?flatpak} to
fix the non-flatpak build.
Unlike the regular package, the flatpak is expected to work on
previous Fedora releases as well. Address this by including the
flathub patch that adds compatibility with previous GNOME versions
when building for the flatpak.
Note that the patch adds a GSettings schema that will break gnome-shell
if both the app and the shell are installed in the same namespace.
