Inconsistency: There is no "front" texture for the hotbar highlight graphic

The bug

For selected items in the hotbar, there is only a "background"-type texture, rendered underneath the item icon. This is inconsistent with the graphics used for inventories and bundles, which have both a "back" and "front" graphic.

How to fix

Add a dedicated "front" texture for the hotbar, which would be blank by default, but customizable via resource packs.