Fix C++ ternary operator type checking for bitfield operands

[tautschnig]

implicit_conversion_sequence does not guarantee to produce the exact type requested as bitfields promote to the underlying type. Therefore, add typecasts as needed to ensure type consistency.

Fixes: #933

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.93%. Comparing base (4fe3ade) to head (1b4ef10).

Files with missing lines	Patch %	Lines
src/cpp/cpp_typecheck_expr.cpp	50.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8792      +/-   ##
===========================================
- Coverage    79.93%   79.93%   -0.01%     
===========================================
  Files         1698     1698              
  Lines       187698   187704       +6     
  Branches        73       73              
===========================================
+ Hits        150034   150037       +3     
- Misses       37664    37667       +3     

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