Implement ed25519 primitives for proposals 220, 224, 228
For proposal 220, we need ed25519 with detached signatures. (#12498 (moved))
For proposal 224 (#12424 (moved)), we need ed25519 with key blinding (#8106 (moved)).
For proposal 228, we need the ability to convert curve25519 keys to ed25519 keys. (#12499 (moved))