Update all NFT contracts stdlib.fc dependencies to available alternatives

[moven0831]

Due to the change of updating stdlib.fc to 'commit 3d9a165 on Oct 25, 2022', many stdlib.fc dependencies in NFT contracts are outdated.

Thus, this pull request contains following change:

1. Change builder_null? to builder_depth
2. Change equal_slices to equal_slice_bits

Above changes have been applied to the following files:

• nft/nft-collection-editable.fc
• nft/nft-collection.fc
• nft/nft-item-editable-DRAFT.fc
• nft/nft-item.fc
• nft/nft-marketplace.fc
• nft/nft-sale.fc
• stdlib.fc (upgrade to commit 3d9a165 on Oct 25, 2022)