CHC solver: use address_of on RHS in counterexample traces

[kroening]

This changes the output of address-of expressions on the right hand side of assignments in counterexample traces to use address_of(...), for improved clarity.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Base: 77.88% // Head: 77.88% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (db722fb) compared to base (4becb88).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7218      +/-   ##
===========================================
- Coverage    77.88%   77.88%   -0.01%     
===========================================
  Files         1616     1616              
  Lines       186720   186728       +8     
===========================================
+ Hits        145433   145438       +5     
- Misses       41287    41290       +3     

Impacted Files	Coverage Δ
src/cprover/report_traces.cpp	89.74% <100.00%> (+0.85%)	⬆️
src/goto-analyzer/static_simplifier.cpp	87.65% <100.00%> (+0.31%)	⬆️
src/util/format_expr.cpp	87.28% <0.00%> (-0.85%)	⬇️

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[tautschnig]

Looks innocent to me, but I have no idea why the CHC solver needs its own facility for producing traces.

[kroening]

Looks innocent to me, but I have no idea why the CHC solver needs its own facility for producing traces.

The existing data structure require iterators into a goto program, but the CHC solver works on a formula.