fix: Preserve padding in tuple-based declarations

[kevinclancy]

Notes

Previously, in a declaration of the form (,uint a, uint b) = ... the leading "padded" position was removed from the AST during a pre-processing step that converted declarations into assignments. The caused the variables a and b to get assigned to components 0 and 1 instead of 1 and 2.

This PR preserves the padding during the AST transformation.

Testing

• Run make test and verify that tests succeed
• Run ./evaluate.sh run 100 in tool-eval and verify that projects succeed.

Try viewing the IR for this test file:

pragma solidity ^0.8.13;

contract Other {
    struct S {
        uint z;
        //uint[] a;
        uint b;        uint c;
        uint d;
    }

    mapping(uint => S) public M;
}

contract Test {
    Other other;

    function test() external {
        (uint z, , uint c, uint d) = other.M(3);
        (z , c, , d) = other.M(3);
    }
}

Related Issue

https://github.com/CertiKProject/slither-task/issues/539
See also: crytic#1913

[duckki]

The code change looked good.
The test clearly showed the problem and the change fixed it.