AngryAt tag is not used by certain neutral mobs, causing them to forget their target upon reloading game

The bug

This is a polished re-submission of MC-256268.

The AngryAt NBT tag is not used by certain neutral mobs. I believe this to be a valid bug, because this causes them to forget their target upon reloading the game. This also causes them to not be affected by commands that modify the AngryAt tag.

Affected mobs

• Dolphin

• Goat (I believe it is technically a passive mob, so this could be WAI)

• Llama

• Panda

• Trader Llama

To reproduce

• Summon an affected mob and hit it.

• Use /data get entity [UUID] AngryAt and see that it does not save the target to NBT.

• Exit the game and enter the game again.

• ❌ The mob has forgotten about the player that hit it.

Alternate reproduction steps

• Run /data merge entity [UUID] {AngryAt:[Your UUID], AngerTime:2000}

• The mob does not target you.