Structure blocks do not mirror certain special entity properties correctly when loading

Saving a structure with a structure block and then loading it with mirroring loads entities with inconsistent mirroring behavior compared to when saved.

Example scenarios that do not handle mirroring:

• Entity LeftHanded-ness
• Armor stand held items
• Armor stand pose (all body parts)
• Falling block state
• Enderman held block state
• Minecart display tile state
• This has edge cases where, for example, stairs would get rotated along with the minecart when mirroring, so some states would not be flipped, like the facing direction, yet others would need to be flipped, like the stairs shape

Other scenarios to consider that might be better off without change

• Item frame item rotation