EIP-7280: NFT Metadata Extension like JSON-LD

I am now working with an airline company to mint NFTs as proofs of carbon-offset flights and trying to expand the project to all companies in the industry.

In terms of the nature of blockchains, we would like to have a long-living and flexible standard for semantic data structure with metadata of NFTs to be used from computers.

On the other hand, I think the basic concept for metadata of NFT should be free.

I found this agenda is like the relationship among HTML and JSON-LD.
So, I designed a loose standard for metadata of NFTs.
Add a new property called linked_data to the top of the tree of NFT metadata JSON.
linked_data contains a array of objects which have both schema and data properties.

I knew that the similar specification is already proposed as ERC-4955.
However, it is not so handy because of its type is object. The future developers should know the entity keys of the object in advance.

In addition, the property name linked_data could make it more clear how to be used.

Pull Request URL is the following: