SMT2: relations on the range type

[kroening]

The range type is encoded using binary (using an offset for negative numbers). This adds support for <, <=, >, >= over the range type to the SMT2 backend.

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• n/a 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).
• 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

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.74%. Comparing base (ee8d275) to head (6109869).
Report is 11 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/solvers/smt2/smt2_conv.cpp	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8523      +/-   ##
===========================================
- Coverage    78.93%   78.74%   -0.19%     
===========================================
  Files         1728     1728              
  Lines       198550   199020     +470     
  Branches     18372    18392      +20     
===========================================
+ Hits        156719   156720       +1     
- Misses       41831    42300     +469     

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