SMT-LIB2: shifts with wider shift distances

[kroening]

This fixes the case of converting shifts where the shift distance is wider than the shift operand to SMT-LIB2.

SMT-LIB2 requires that the width of the shift operand and the shift distance is the same. To not lose leading bits of the shift distance, use the wider one of the two as the width of the shift, and truncate the result when needed.

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[codecov]

Codecov Report

❌ Patch coverage is 98.68421% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.01%. Comparing base (15eb10a) to head (a136328).

Files with missing lines	Patch %	Lines
src/solvers/smt2/smt2_conv.cpp	97.61%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8834   +/-   ##
========================================
  Coverage    80.00%   80.01%           
========================================
  Files         1700     1700           
  Lines       188252   188312   +60     
  Branches        73       73           
========================================
+ Hits        150613   150675   +62     
+ Misses       37639    37637    -2     

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