SMT2: implement range type

[kroening]

This adds missing support for encoding the range_typet 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 5.55556% with 34 lines in your changes missing coverage. Please review.

Project coverage is 78.22%. Comparing base (d2b4455) to head (e21c686).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/solvers/smt2/smt2_conv.cpp	5.55%	34 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8466      +/-   ##
===========================================
- Coverage    78.31%   78.22%   -0.10%     
===========================================
  Files         1726     1726              
  Lines       188817   189038     +221     
  Branches     18270    18265       -5     
===========================================
  Hits        147874   147874              
- Misses       40943    41164     +221     

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[peterschrammel]

Is there something that is going to test this?

[kroening]

Is there something that is going to test this?

Not easy -- the only language I know where this is of use are SMV and VHDL.

I think I want to make the architecture of the decision procedure and the simplifier we have more modular, enabling us to plug these in where they are needed.