Support for EIP-1271 signatures

[frangio]

EIP-1271 is a standard to grant smart contracts the ability to sign messages. This is useful to support smart contract wallets like Argent or Gnosis Safe in applications that make use of signatures. Ethers.js could support this EIP by providing a signature verification utility function that can check both EOA and EIP-1271 signatures, similar to OpenZeppelin's SignatureChecker. As opposed to EOA signature recovery this function would require a provider, but I'd imagine it's not so different from ENS resolution support.

[xinbenlv]

This is already done, right? Strike that.

Right, ethers-js doesn't support 1271 out of box at v5 or v6.
Agree with @frangio that having a native support for ERC-1271 will be great