Sun texture appears mirrored in-game

Discovered while testing MC-241035, and closely relates to MC-241006.

The bug

The texture used for the sun appears horizontally flipped when seen in-game compared to how it is as a file. This is generally impossible to see without a texture pack given the vanilla texture's symmetry, but becomes all the more apparent when a custom, non-mirror-symmetric texture is used.

How to reproduce

1. Download and apply the testing texture pack attached to MC-241035
2. Look at the sun

Expected results

The text inside the image would be readable normally from left-to-right.

Actual results

The text appears flipped horizontally from what it should be.