Custom Blocks Don't Register

All custom blocks are currently broken in the 1.20 betas.

Steps To Reproduce:

• Download the supplied addon
• Load a world with the pack and all relevant experiments on (I have them all on for my main pack)
• Observe a content log error for Iron Block Slab
• Observe that it is also not in the creative inventory and cannot be given through commands

Observed Results:

• Custom blocks are currently completely broken in the 1.20 betas

Expected Results:

• Custom blocks register in the game properly and the schema isn't 'unrecognised'