Use get_writeable_symbol() to avoid redundant search

[tautschnig]

Don't iterate over a symbol table and then search the symbol we hold an iterator to from scratch. Just use our custom iterators instead of ranged for loops to directly access a writeable version of the symbol.

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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/
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[codecov]

Codecov Report

Patch coverage: 88.17% and project coverage change: -0.02 ⚠️

Comparison is base (2c5a2e5) 78.50% compared to head (4a93fcf) 78.48%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7615      +/-   ##
===========================================
- Coverage    78.50%   78.48%   -0.02%     
===========================================
  Files         1670     1670              
  Lines       191802   191802              
===========================================
- Hits        150575   150544      -31     
- Misses       41227    41258      +31     

Impacted Files	Coverage Δ
src/cpp/cpp_typecheck_template.cpp	72.70% <25.00%> (-0.22%)	⬇️
src/cpp/cpp_typecheck_declaration.cpp	73.25% <50.00%> (+0.84%)	⬆️
...code/java_bytecode_concurrency_instrumentation.cpp	96.58% <60.00%> (ø)
src/goto-cc/linker_script_merge.cpp	79.02% <87.50%> (+0.10%)	⬆️
src/goto-instrument/dump_c.cpp	80.09% <88.88%> (+0.11%)	⬆️
src/ansi-c/c_typecheck_type.cpp	77.02% <100.00%> (-0.03%)	⬇️
src/cpp/cpp_typecheck.cpp	77.27% <100.00%> (-0.30%)	⬇️
src/cpp/cpp_typecheck_expr.cpp	71.83% <100.00%> (-0.10%)	⬇️
src/goto-programs/name_mangler.h	98.48% <100.00%> (+0.02%)	⬆️
src/goto-programs/remove_complex.cpp	87.50% <100.00%> (+0.08%)	⬆️
... and 5 more

... and 1 file with indirect coverage changes

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[peterschrammel]

👍