Scrollers in block UIs render translucent pixels as opaque

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

The bug

The scroll rectangles in the Creative inventory and in loom, stonecutter and villager GUI screens will render any translucent pixels in their textures as fully opaque. This is in contrast to the scrollers in menu screens, which will correctly render any translucent pixels as translucent (except for incongruous cases MC-269619, MC-269755 and MC-269763).

This was previously covered under MC-165182.

How to reproduce

1. Download and apply the attached resource pack

2. Enter a loom, stonecutter or villager GUI or the Creative inventory

3. Look at the scroll bars

Expected results

Translucency.

Actual results

Complete and utter opacity.