Minecraft generates mipmapped textures for banners, but does not use them

Relates to: MC-276568 MC-277447 MC-277450 MC-277470 MC-277471 MC-277473

The bug

When loading the game's resources, Minecraft generates mipmapped textures for all banner-related textures. 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. Place several blank banners

3. Place white wool

4. Compare

Expected results

The banners would fade into a smooth gray in the distance, much like the wool.

Actual results

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

How to fix

Either make banners use mipmapping like other blocks (easily doable if they get converted over to use proper block models), or don't generate these mipmapped textures for banners at all. Several other atlases (gui, map decorations, mob effects, paintings, particles) don't generate mipmapped versions of themselves, so why should banners if they're not going to be used?