Add incremental SMT support for struct with and member expressions

[thomasspriggs]

This PR adds incremental SMT support for struct with and member expressions.

• 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.
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Patch coverage: 98.66% and project coverage change: +0.06 🎉

Comparison is base (da48fba) 78.58% compared to head (c4ccf66) 78.64%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7787      +/-   ##
===========================================
+ Coverage    78.58%   78.64%   +0.06%     
===========================================
  Files         1693     1697       +4     
  Lines       193381   193894     +513     
===========================================
+ Hits        151962   152491     +529     
+ Misses       41419    41403      -16     

Impacted Files	Coverage Δ
...olvers/smt2_incremental/encoding/struct_encoding.h	100.00% <ø> (ø)
..._incremental/smt2_incremental_decision_procedure.h	75.00% <ø> (ø)
...ncremental/smt2_incremental_decision_procedure.cpp	95.73% <94.11%> (-0.51%)	⬇️
...vers/smt2_incremental/encoding/struct_encoding.cpp	95.04% <96.96%> (+5.86%)	⬆️
...vers/smt2_incremental/encoding/struct_encoding.cpp	100.00% <100.00%> (ø)

... and 18 files with indirect coverage changes

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