Horses can suffocate when going through nether portals

Everytime I push a horse through a nether portal and it comes to the other dimension, it suffocate in obsidian or in surrounding blocks. Sometime, I can't get out of it an dies.

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Note that this may actually be three bugs:

• Horses can suffocate from walls because they are partially teleported into them
• Players can push horses into the obsidian wall after portal teleport
• Horse size is not accounted for when placing horse inside the portal (MC-121098)

This ticket only describes the first two bugs, which should be properly tested and split into two tickets at some point.