move gstreamer backend to -media-gstreamer subpkg
GStreamer is pretty huge dependency that is needed only for some applications. For example, Debian provides it in a separate package (libgtk-4-media-gstreamer) too.
gtk4.0-media-gstreamer should be added as a dependency to the packages that actually need it. Unfortunately, I don't know which ones are they at this moment.
Already merged
move dev tools and valgrind .supp to -dev subpkg
gtk4-builder-tool, gtk4-encode-symbolic-svg, gtk4-query-settings are not needed for running applications (as I know), these are development tools. For example, Fedora provides them in subpackage gtk4-devel, Debian in libgtk-4-bin.
This decreases size of the gtk4.0 package from 16.4 MiB to 9.0 MiB.
move localized emoji labels to -lang subpkg
This will reduce size of the gtk4.0 package from 9 MiB to 8.6 MiB.