Extend support for binding expressions beyond quantifiers

[tautschnig]

Symex special-cased some code for quantifiers when really all binding
expressions have to be treated that way. To support this, add
can_cast_expr<binding_exprt>, and make sure all subclasses of
binding_exprt are covered by this cast.

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[codecov]

Codecov Report

Base: 77.99% // Head: 77.99% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (4a15cf0) compared to base (9baef8f).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 4a15cf0 differs from pull request most recent head 6f8a7b8. Consider uploading reports for the commit 6f8a7b8 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #6810   +/-   ##
========================================
  Coverage    77.99%   77.99%           
========================================
  Files         1619     1619           
  Lines       187184   187189    +5     
========================================
+ Hits        145999   146004    +5     
  Misses       41185    41185           

Impacted Files	Coverage Δ
src/goto-symex/symex_clean_expr.cpp	93.16% <100.00%> (ø)
src/goto-symex/symex_dereference.cpp	89.89% <100.00%> (+0.10%)	⬆️
src/util/std_expr.h	93.15% <100.00%> (+0.01%)	⬆️

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[kroening]

It may be appropriate to consider what the code is doing when dealing with a binding -- my understanding is that all it does is disabling the caching of dereferenced expressions, right?

[tautschnig]

It may be appropriate to consider what the code is doing when dealing with a binding -- my understanding is that all it does is disabling the caching of dereferenced expressions, right?

Yes, because there's a risk of having to deal with bound variables that the code is not prepared to deal with.

[kroening]

Note that there are also let_exprt -- unfortunately these aren't derived from binding_exprt (since they don't satisfy the invariants of these).

[tautschnig]

Note that there are also let_exprt -- unfortunately these aren't derived from binding_exprt (since they don't satisfy the invariants of these).

I have now added a check for these when computing is_binding_expression.