add mulit-ary constructor for xor_exprt, bitxor_exprt, bitand_exprt, …

[kroening]

This adds a constructor that takes an exprt::operandst argument, for constructing xor_exprt, bitxor_exprt, bitand_exprt, bitor_exprt with more than two operands.

• 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

All modified and coverable lines are covered by tests ✅

Project coverage is 78.93%. Comparing base (e186314) to head (923769f).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8529      +/-   ##
===========================================
+ Coverage    78.85%   78.93%   +0.08%     
===========================================
  Files         1728     1728              
  Lines       198844   198634     -210     
  Branches     18385    18309      -76     
===========================================
  Hits        156795   156795              
+ Misses       42049    41839     -210     

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