Update the icon for GNOME Firmware and more

[morganist]

Updated GNOME Firmware icon to a new version (closes #2392):

It is based on the Gtkstresstesting icon, but recoloured to represent a green pcb instead of a red one;
Introduced gst.svg (copied from com.leinardi.gst.svg);
Made gst.svg the main Gtkstresstesting icon because it is the name of its native (non-flatpak) executable;
Tweaked gst.svg (Gtkstresstesting icon): tweaked shadows, added a shadow and an outline on the chip;
Symlinked com.leinardi.gst.svg to gst.svg;
Introduced gnome-firmware.svg (copied from com.gnome.Firmware.svg);
Made gnome-firmware.svg the main GNOME Firmware icon because it is the name of its native (non-flatpak) executable;
Symlinked firmware-manager.svg and application-x-firmware.svg to gnome-firmware.svg instead of com.gnome.Firmware.svg;
And of course, symlinked com.gnome.Firmware.svg to gnome-firmware.svg;

[morganist]

Is this even the right way to symlink things? I don't quite understand the difference between executable names, desktop file names and flatpak apps names. But in general i see that the majority of icons is named like their executable names, not flathub/flatpak/desktop filenames - these are symlinked. It is quite hard, to be honest... I just want to help clearing this mess up.

[SmartFinn]

@morganist no matter what name you use for an icon, or what you use for symlink. But when you choose between a common name (e.g. disk-usage-analyzer) and an app name (e.g. filelight), the common name should be chosen.

[morganist]

i just think it simplefies things — it is easier to search for an icon when the source icon (not a symlink) is not named "comnetorg.developer.longappname" or something

[SmartFinn]

I'll be preferred to keep the old org.gnome.Firmware.svg icon as application-x-firmware.svg. I'll do it myself, so there's no need to do anything.