Add implementation of smt2_incremental_decision_proceduret::get

[thomasspriggs]

This PR adds the implementation of smt2_incremental_decision_proceduret::get. This adds enough functionality to allow printing of traces and performing incremental solving.

• 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

Merging #6573 (8348994) into develop (bd1401f) will increase coverage by 0.02%.
The diff coverage is 91.35%.

❗ Current head 8348994 differs from pull request most recent head a3f6bd4. Consider uploading reports for the commit a3f6bd4 to get more accurate results

@@             Coverage Diff             @@
##           develop    #6573      +/-   ##
===========================================
+ Coverage    75.99%   76.01%   +0.02%     
===========================================
  Files         1579     1579              
  Lines       181124   181368     +244     
===========================================
+ Hits        137643   137875     +232     
- Misses       43481    43493      +12     

Impacted Files	Coverage Δ
...ncremental/smt2_incremental_decision_procedure.cpp	88.88% <79.41%> (-1.04%)	⬇️
...ncremental/smt2_incremental_decision_procedure.cpp	96.47% <100.00%> (+0.92%)	⬆️
src/solvers/sat/satcheck_minisat2.h	75.00% <0.00%> (-9.22%)	⬇️
src/util/symbol_table_builder.h	56.66% <0.00%> (-6.67%)	⬇️
src/util/std_types.cpp	85.71% <0.00%> (-1.65%)	⬇️
jbmc/src/java_bytecode/java_pointer_casts.cpp	92.50% <0.00%> (-0.84%)	⬇️
src/solvers/flattening/boolbv_get.cpp	82.03% <0.00%> (-0.72%)	⬇️
src/util/std_types.h	95.01% <0.00%> (-0.57%)	⬇️
src/ansi-c/expr2c.cpp	65.94% <0.00%> (-0.46%)	⬇️
...trument/contracts/havoc_assigns_clause_targets.cpp	97.72% <0.00%> (-0.35%)	⬇️
... and 44 more

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[TGWDB]

LGTM

[NlightNFotis]

LGTM.