Entity collisions fully above an entity's hitbox are ignored when stepping up blocks

When an entity is stepping up blocks, the client code fully ignores any entity collisions which are fully above the hitbox of the entity performing the step up.

I have provided 3 different scenarios, where this leads to reproducable “glitchy” behaviour.

1. By riding a pig with a carrot on a stick into a block with a shulker on top as seen in shulker_pig.mp4

2. By stepping into a 1.5 block tall gap underneath a shulker as seen in shulker.mp4 (make sure to either use the command tick freeze or spawn a shulker with {NoAI:1b} so it stays in place)

3. By increasing the step height and stepping up a stack of blocks with a boat/shulker on top as in boat.mp4 (here I increased by step_height attribute to 2.

Possibly a fix of this could be combined with a fix/improvement of MC-260743.