Riding position for the llama is offset, which can lead to suffocation near walls

The riding position of the llama is offset, which causes unexpected behavior such as; suffocating in walls, appearing to sit on/in the llama's neck, or appearing to sit on the edge of the llama.

Steps to Reproduce:

1. Spawn a tamed llama:

   /summon llama ~ ~ ~ {Tame:1b}
   

2. Ride it
3. Enable hitboxes using F3 +B
4. Allow the llama to move around freely

Expected & Observed Results:

- The player will rotate around on top of the llama at an offset, and appear in weird positions/rotations. If the player riding the llama is next to a wall, they may suffocate as their hitbox is put inside blocks.
- The player (or general entity) would ride in the relative middle of the top of the llama's hitbox.

Screenshots/Videos:

Minecraft 20w51a - Singleplayer 2020-12-31 17-07-00_Trim.mp4

Notes:

This issue used to specifically be about the llama causing suffocation damage when riding next to a wall, but the issue was generified in favor of describing the issue in a more broad way, at the source of the issue.