Minecraft generates mipmapped textures for shulker boxes, but does not use them

Relates to MC-276568 and MC-277447.

The bug

When loading the game's resources, Minecraft generates mipmapped textures for all types of shulker box. However, it does not use them at all, wasting game resources.

How to reproduce

A resource pack is attached to this ticket.

1. Download and apply the attached resource pack

2. /fill ~ ~ ~ ~60 ~ ~60 minecraft:shulker_box

3. /fill ~ ~ ~ ~60 ~ ~60 minecraft:purpur_block

4. Compare

Expected results

The shulker boxes would fade into a smooth gray in the distance, much like the purpur does.

Actual results

No such thing happens and we get incredibly grainy Moire patterns.

How to fix

Either make shulker boxes use mipmapping like other blocks (easily doable if MC-276881 gets fixed), or don't generate these mipmapped textures for shulker boxes at all. Several other atlases (gui, map decorations, mob effects, paintings, particles) don't generate mipmapped versions of themselves, so why should shulker boxes if they're not going to be used?