BLS12-381 precompile implement

[hujw77]

BLS precompile facilitate eth2.0 light client to verify BLS signature.
There are two ways to reach the goal.

Wrap BLS lib

BLS precompile should implement the interface below:

interface BLS {
        function FastAggregateVerify(
            bytes[] calldata pubkeys,                    // BLS public keys
            bytes calldata message,                    // Message to be verify
            bytes calldata signature                   // BLS Aggregated signature
        ) external pure returns (bool);             // Return valid or invalid
}

Rust lib refer: https://github.com/sigp/milagro_bls

EIP-2537

https://eips.ethereum.org/EIPS/eip-2537

[hujw77]

ethereum/pm#343