Buttons in the beacon GUI do not support translucent pixels

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

The bug

If the textures used for buttons in the beacon UI contain translucent pixels, these will be rendered completely opaque in-game.

The same also goes for status effect icons, which are otherwise rendered fine in the HUD - see MC-174732.

How to reproduce

1. Download and apply the attached resource pack
2. Enter a beacon
3. Observe

Expected results

Translucent buttons.

Actual results

Entirely opaque.