99d49c1800
PopupImageMenuItems used to position the icon after the label,
so we ended up with our own icon+label items.
However the icon position was changed years ago in the shell, so
inherit from PopupImageMenuItem instead.
This does not only simplify the code a bit, but also pulls in
features we are currently missing, like a11y labelling.
Closes: https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/issues/542
(cherry picked from commit 568826e489)