Fix builtin function return hidden flag inconsistency

[tautschnig]

Function returns for built-in functions now correctly match their function call hidden flag. This is done by symex storing the combined hidden flag in call frame.

Co-authored-by: Kiro autonomous agent

Fixes: #5207

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.01%. Comparing base (76dd20f) to head (64d8732).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8800   +/-   ##
========================================
  Coverage    80.00%   80.01%           
========================================
  Files         1700     1700           
  Lines       188249   188249           
  Branches        73       73           
========================================
+ Hits        150615   150620    +5     
+ Misses       37634    37629    -5     

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