[1.21] Add EMI compat.

[ChrysanthCow]

Resolves #877

The main difficulty here was translating every tag, but ideally, you won't have to change the tags again.

Check #971 if you want to see the general difference in updating.

EMI has a really good API, so I'd imagine updating wouldn't be too painful, but ultimately, it's your call whether this gets in or not.