Refactor SMT solver process class heirarchy

[thomasspriggs]

The previously merged PR here introduced some code duplication in between two classes in the hierarchy - #7161

This PR is a potential way to eliminate the duplication, which should make maintenance less error prone than maintaining the multiple code duplicates.

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• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
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• 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).
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[codecov]

Codecov Report

Base: 78.38% // Head: 78.38% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (9312a53) compared to base (3a1a5ac).
Patch coverage: 91.11% of modified lines in pull request are covered.

❗ Current head 9312a53 differs from pull request most recent head f6ac7ab. Consider uploading reports for the commit f6ac7ab to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7431   +/-   ##
========================================
  Coverage    78.38%   78.38%           
========================================
  Files         1655     1655           
  Lines       190304   190334   +30     
========================================
+ Hits        149166   149192   +26     
- Misses       41138    41142    +4     

Impacted Files	Coverage Δ
src/goto-checker/solver_factory.h	100.00% <ø> (ø)
...ncremental/smt2_incremental_decision_procedure.cpp	98.59% <0.00%> (ø)
src/solvers/smt2_incremental/smt_solver_process.h	71.42% <33.33%> (-28.58%)	⬇️
src/goto-checker/solver_factory.cpp	81.81% <82.35%> (+0.05%)	⬆️
src/ansi-c/c_typecheck_base.cpp	83.10% <85.71%> (ø)
src/goto-instrument/contracts/contracts.cpp	95.38% <100.00%> (ø)
src/goto-programs/builtin_functions.cpp	60.68% <100.00%> (ø)
...c/solvers/smt2_incremental/convert_expr_to_smt.cpp	83.48% <100.00%> (ø)
...rc/solvers/smt2_incremental/smt_solver_process.cpp	84.12% <100.00%> (+4.96%)	⬆️
src/util/lower_byte_operators.cpp	92.76% <100.00%> (ø)
... and 5 more

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[tautschnig]

The Windows tests are now failing ("Output file does not match.")

[thomasspriggs]

I am going to close this PR out, as I am not currently planning to do further work on it.