Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
Bukkit Changes:
7634491f Added Entity#setRotation.
CraftBukkit Changes:
0e1cea5a Added Entity#setRotation.
This code could get hit by many threads at once, causing multiple
chunk loads to convert legacy data, leading to all sorts of fun.
Additionally, go ahead and preload it async on world load.
Allows you to return the SpawnReason for why an Entity Spawned
Pre existing entities will return NATURAL if it was a non
persistenting Living Entity, SPAWNER for spawners,
or DEFAULT since data was not stored.
Zach Brown
Aikar