[soltest] Add support for left-aligned hex literals

[erak]

Part of #4223.

• Change base branch to develop after [soltest] Create dedicated formatting #6060 got merged

This PR aims to add support for hex literals in (i)soltest. Hex literals result in a left-aligned, padded 32-byte representation:

contract C {
    function g(uint x, uint y) public returns (uint) {
        return x - y;
    }
    function x(bytes32 b) public returns (bytes32) {
        return b;
    }
}
// ----
// g(uint256,uint256): 1, -2 -> 3
// x(bytes32): 0x31 -> 0x31

Decimal number literals are still right-aligned, padded 32 bytes.

This PR also moves some code that is shared between the Solidity parser and the soltest parser.

[codecov]

Codecov Report

Merging #6036 into develop will increase coverage by 0.03%.
The diff coverage is 97.56%.

@@             Coverage Diff             @@
##           develop    #6036      +/-   ##
===========================================
+ Coverage    88.66%   88.69%   +0.03%     
===========================================
  Files          368      368              
  Lines        34956    35031      +75     
  Branches      4131     4133       +2     
===========================================
+ Hits         30992    31070      +78     
+ Misses        2573     2568       -5     
- Partials      1391     1393       +2

Flag	Coverage Δ
#all	88.69% <97.56%> (+0.03%)	⬆️
#syntax	27.82% <4.87%> (-0.05%)	⬇️

[erak]

Updated. Hex number literals with an odd number of digits now throw an exception and character checking is shared in the langutil namespace.

[erak]

Will push an update very soon, that does not decrease coverage.

[erak]

Rebased.