[Experimental] - Snow Layers Can Be Placed / Generate On Non-Full Custom Blocks

When creating custom blocks with non-full collision boxes, snow layers will generate atop them if they are placed with world generation and snow layers can also be placed on these blocks.

See attached image:

• The snow layers have generated on the slabs atop the tower (these slabs are custom slabs)
• They also generate on the blocks next to the campfire

Note: This also extends to other blocks such as vines

Steps To Reproduce:

1. Create a block with a custom hitbox
2. Generate this block throughout snow biomes
3. Observe snow layers generate atop this block
4. Place a snow layer atop this block and observe that it will place

Expected Results:

• Snow layers cannot exist atop blocks with custom entity hitboxes that are smaller than a full block high (Or perhaps a new component allow_snow_layer could be added?)

Observed Results:

• Snow layers can generate and be placed on custom blocks with non-full collision boxes