Slot highlight texture for sliding/dragging items is not editable

When sliding items (click and hold whilst dragging), a slot highlight texture seperate to slot_highlight_front.png or slot_highlight_back.png is used. It is not found anywhere in the game's assets and so is not currently editable via a resource pack.

Attactched image is an example of a resource pack that changes slot_highlight_front/back.png, showing that the dragging icon highlight is unchanged.