fix expr2c on lambda expressions

[kroening]

Lambda expressions are not quantifier expressions, but both quantifier expressions and lambda expressions are bindings. This commit fixes the conversion of lambda expressions to C syntax by generalizing the conversion of quantifier expressions to binding expressions.

• Each commit message has a non-empty body, explaining why the change was made.
• 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

Merging #7137 (f20515f) into develop (9a14d1a) will increase coverage by 0.00%.
The diff coverage is 45.00%.

@@           Coverage Diff            @@
##           develop    #7137   +/-   ##
========================================
  Coverage    77.86%   77.86%           
========================================
  Files         1576     1576           
  Lines       181808   181805    -3     
========================================
- Hits        141573   141571    -2     
+ Misses       40235    40234    -1     

Impacted Files	Coverage Δ
src/ansi-c/c_typecheck_expr.cpp	74.17% <0.00%> (ø)
src/ansi-c/expr2c_class.h	100.00% <ø> (ø)
src/ansi-c/goto_check_c.cpp	91.65% <0.00%> (ø)
src/util/pointer_expr.h	80.83% <0.00%> (ø)
src/ansi-c/expr2c.cpp	67.18% <85.71%> (+<0.01%)	⬆️
src/solvers/flattening/boolbv_mod.cpp	93.33% <100.00%> (ø)

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