Add saturating arithmetic support to SMT2 incremental solver

[tautschnig]

Implements conversion of saturating_plus and saturating_minus expressions to SMT formulas for both signed and unsigned bit-vector types.

Fixes: #8070

• 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

❌ Patch coverage is 97.43590% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.01%. Comparing base (1505c36) to head (cd4d55c).

Files with missing lines	Patch %	Lines
...c/solvers/smt2_incremental/convert_expr_to_smt.cpp	97.43%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8774   +/-   ##
========================================
  Coverage    80.00%   80.01%           
========================================
  Files         1700     1700           
  Lines       188254   188336   +82     
  Branches        73       73           
========================================
+ Hits        150615   150695   +80     
- Misses       37639    37641    +2     

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