Fix incorrect state mutability identification

[0xGeorgii]

This PR fixed incorrect state mutability identification for the various structures, such as:

const state mutability for the state variable declaration

contract Example {
    uint256 constant x = 1;
}

payable state mutability for the function return parameter variable declaration

function test() public returns(address payable) {}

Now, these cases are handled correctly after the bug in the version 0.0.3.