[soltest] Add support for boolean literals

[erak]

Part of #4223.

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

contract C {
    function g(bool x) public returns (bool) {
        return !x;
    }
}
// ----
// g(bool): true -> false

[codecov]

Codecov Report

Merging #6072 into develop will increase coverage by <.01%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           develop   #6072      +/-   ##
==========================================
+ Coverage    88.69%   88.7%   +<.01%     
==========================================
  Files          368     368              
  Lines        35038   35089      +51     
  Branches      4133    4137       +4     
==========================================
+ Hits         31078   31124      +46     
- Misses        2568    2569       +1     
- Partials      1392    1396       +4

Flag	Coverage Δ
#all	88.7% <88.88%> (ø)	⬆️
#syntax	27.79% <6.34%> (-0.03%)	⬇️