media-fonts/cantarell: add missing appstream-glib build dep

media-fonts/cantarell: add missing appstream-glib build dep

During i18n.merge_file() build rule, gettext msgfmt gets called by a meson
script. This in turn looks for ITS rules on how to merge in translations for
a given file. appstream-glib provides /usr/share/gettext/its/appdata.loc,
which tells gettext how to handle *.metainfo.xml files (that in turn points
at appdata.its, also installed by appstream-glib). If that file isn't present
at build time, then gettext errors out due to not knowing how to handle
*.metainfo.xml translation.
As such, we need appstream-glib at build time here, and in various other
packages that have a metainfo/appdata translation in meson.

Closes: https://bugs.gentoo.org/656710
Package-Manager: Portage-2.3.48, Repoman-2.3.10