Banner pattern textures are noticeably asymmetric

Relates to MC-260657 and MC-275334.

The bug

The shape of banner patterns as of the 1.21.2 snapshots are very asymmetric; the left hand side gets wider two pixels down, but the right does at four pixels down.

This is particularly obvious in the loom GUI.

How to fix

Change the textures of banner patterns so that they appear more symmetric in this respect.