Add tag aliases

[Juuxel]

The tag alias API lets modders merge different but equivalent tags together so that they have the same content. For example, tag aliases can be used to unify matching minecraft and c tags. (This is the main purpose of the PR.)

Tag aliases are defined in data packs like tags. For example, a block tag alias group for fences would be located at data/my_mod/fabric/tag_aliases/block/fences.json with the contents:

{
  "tags": [
    "minecraft:fences",
    "c:fences"
  ]
}

The files can also be generated with the data generation API. Alias groups can be replaced (or disabled) like most data pack files by having a different file with the same name at the same file path.

TODO:

• Better docs
• Tests
  • Functionality
  • Data generation