(24w33a - 24w36a) Highlighted bundle slot

[muzikbike]

Much like in #55, the square displayed for whatever item is highlighted in bundles as of 24w33a's rework was a hardcoded graphic, only made customizable in 24w37a. It also uses the behind-and-above system of two textures, only in this case the above texture is invisible and it is the behind texture we see by default.