OP_TWEAKADD - x-only key tweak addition.

Would add a script command that adjusts a public key by a given number, the same way Taproot adjusts keys.

Taproot already 'tweaks' keys, but a script can't do this itself. OP_TWEAKADD would let a script work out a tweaked public key and keep using it, without revealing private keys or relying on hash locks. It is aimed at contracts such as delegation and proving the order in which people signed.