Consider supporting Gstreamer GTK4 plugin

Hi, first of all, thanks a lot for maintaining this project! I had so much trouble getting Gtk4 set up on Windows using MSYS2. Gvsbuild just works 🙂 I only have one Gtk4 dependency which I still have to build myself after running gvsbuild: Gstreamer GTK4 plugin. It would be great if I could build this plugin with gvsbuild as well. I am currently installing this plugin after gvsbuild like so: ```Powershell # Get GStreamer version we built earlier with gvsbuild to make sure we build a compatible version of the plugin $env:gstreamer_version = (gvsbuild.exe list --json | ConvertFrom-Json).psobject.Properties.Where({ $_.Name -eq "gstreamer" }).Value.version git clone https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs.git -b gstreamer-$env:gstreamer_version cd gst-plugins-rs cargo install cargo-c cargo cinstall -p gst-plugin-gtk4 --prefix ($project + "\build\gtk\x64\release") --libdir ($project + "\build\gtk\x64\release\lib") # Now run `gst-inspect-1.0.exe gtk4paintablesink`. If it does not return an error everything went fine. ``` Here are some links: * Upstream: https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/tree/main/video/gtk4?ref_type=heads * ArchLinux package: https://archlinux.org/packages/extra/x86_64/gst-plugin-gtk4/ * Debian package: https://packages.debian.org/trixie/gstreamer1.0-gtk4