[MCPE-186357] Skull block IDs flattened incorrectly

Skulls were not flattened to the same block IDs as Java Edition, similar to double slabs (MCPE-178372) and light blocks (MCPE-183450).

Expected Result

Skulls are flattened into two block IDs: a floor and wall version.

Original ID	Data Value	Flattened IDs
skull	0	skeleton_skull skeleton_wall_skull
skull	1	wither_skeleton_skull wither_skeleton_wall_skull
skull	2	zombie_head zombie_wall_head
skull	3	player_head player_wall_head
skull	4	creeper_head creeper_wall_head
skull	5	dragon_head dragon_wall_head
skull	6	piglin_head piglin_wall_head

This allows commands to place a skull on the floor facing a specific direction, which is currently impossible on Bedrock.

Observed Result

Skulls were flattened into one block ID which covers both the floor and wall variants.

This makes it impossible for commands to place a skull on the floor facing a specific direction.