Assorted Resource Pack Fixes

[runcows]

• Add overlay for pre 1.21.9 models (fixing spyglass and trident)
• Add particle textures for all models I could find that needed them
• Move blocks atlas to new items and overlay it
  • also remove the entity import. I'm not sure if it was used, since there's not errors without it

I'd want to fix the Data Pack / Resource Pack overlay field mixing issues we're having as well, but I don't exactly know how