Simplify quantified expressions over constants

[tautschnig]

Other simplification rules may turn the where-clause of a quantified expression into a (Boolean) constant. We can completely remove such quantified expressions so as not to distract back-ends that may special-case quantified expressions.

We saw such expressions when working on mlkem-native.

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• 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).
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[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.63%. Comparing base (32143dd) to head (03ed18f).

Files with missing lines	Patch %	Lines
src/util/simplify_expr_boolean.cpp	88.88%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8608      +/-   ##
===========================================
+ Coverage    79.17%   79.63%   +0.45%     
===========================================
  Files         1733     1733              
  Lines       198963   197848    -1115     
  Branches     17967    18199     +232     
===========================================
+ Hits        157536   157562      +26     
+ Misses       41427    40286    -1141     

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[kroening]

It's unfortunately not that easy: The domain may be empty, and then ∀x.false is true, and ∃x.true is false.