Advancement frames render translucent pixels as opaque

More loosely relates to these issues: MC-144009 MC-145821 MC-164001 MC-165403

The bug

The textures used for the backgrounds of advancement icons will render any translucent pixels in their texture files as completely opaque.

How to reproduce

1. Download and apply the attached resource pack
2. Look in the advancements menu

Expected results

The icon backgrounds would be translucent.

Actual results

They are solid opaque squares.

How to fix

Permit translucent textures in this context.