Add string literal support to incremental SMT decision procedure

[thomasspriggs]

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (cafe331) 78.67% compared to head (3f7e416) 78.68%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7808      +/-   ##
===========================================
+ Coverage    78.67%   78.68%   +0.01%     
===========================================
  Files         1699     1699              
  Lines       194122   194172      +50     
===========================================
+ Hits        152719   152791      +72     
+ Misses       41403    41381      -22     

Impacted Files	Coverage Δ
..._incremental/smt2_incremental_decision_procedure.h	75.00% <ø> (ø)
...ncremental/smt2_incremental_decision_procedure.cpp	95.82% <100.00%> (+0.08%)	⬆️
...ncremental/smt2_incremental_decision_procedure.cpp	98.73% <100.00%> (+0.09%)	⬆️

... and 2 files with indirect coverage changes

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[NlightNFotis]

I think the reason CI fails is this needs to be either <util/string_constant.h> or there must be a string_constant.h header somewhere else that hasn't been included with this PR.

Either way, an easy fix.

[thomasspriggs]

Quite likely.