Add support for prevrandao

[0xalpharush]

For EVM versions paris and later, difficulty was replaced by prevrandao

contract C {
    function f() public view returns (uint256) {
        return block.prevrandao;
    }

    function g() public view returns (uint256 ret) {
        assembly {
            ret := prevrandao()
        }
    }
}

[kamenik]

Would be nice, lost few hours trying to use slither with my, too new, code:/.