Add a replacement for the definition field in blocks.json data report.

In the game's data generators, the definition field of blocks.json was a really convenient way to map out the block types of any given block in the game, and use the block type itself to infer data about the blocks, which is used in balancing custom content in places like datapacks and mods that are built close to vanilla's design philosophy.

You said that everything when removed, there'll always be a proper replacement for it, yet in this specific case, there wasn't anything like it. It is very frustrating to see promises being broken like this.

Now, the only way to do that is to go through the code itself to figure all that out again, which means having to rebuilt the system that's gathering this data from scratch.

Super annoying that there's been no proper replacement to this.

EDIT: You can't even get a block's type anymore because undocumented in 26.3's Changelogs, the block type registry has been completely obliterated.