Revisit canWalkOn / canWalkThrough checks

For example, decide whether end rods and flower pots should really be canWalkThrough since they do collide (even in a small way).

Should we make shulker boxes canWalkOn even though they expand when opened?

In general, should canWalkOn's bounding box check be changed to only do the Y coordinate? Or maybe something smarter...

Should anvils be canWalkOn?

Should grass_path and farmland be canWalkOn?

Should glass be canWalkOn?

Magma should probably be a separate check due to the sneaking cost, it's good that it's not canWalkOn