Shift+Click; extending lists not duplicating Ctrl+Click add to list

Spawning off a discussion from fix #10763 by @Cattlesquat :

Shift+Click to extend a selection on a palette would make sense to me, as the palette is effectively a list. Also, in a GPIW if it came to it. I don’t see the point on a map though, especially as that interferes with Shift+Click for other things, like selecting a “Do Not Stack” piece. I think I’ve raised this before, so apologies if it was already decided against (maybe some constraint like VASL dependency?).