Rewrite use of *_nonconst()

[tautschnig]

Construct instructions with the intended value right away rather than fixing them up afterwards.

Requires #6420 to be merged first.

• 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.
• 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).
• 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

Base: 77.89% // Head: 77.92% // Increases project coverage by +0.03% 🎉

Coverage data is based on head (bdc007a) compared to base (ef481c4).
Patch coverage: 74.88% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6421      +/-   ##
===========================================
+ Coverage    77.89%   77.92%   +0.03%     
===========================================
  Files         1616     1616              
  Lines       186793   186762      -31     
===========================================
+ Hits        145498   145531      +33     
+ Misses       41295    41231      -64     

Impacted Files	Coverage Δ
src/analyses/interval_analysis.cpp	0.00% <0.00%> (ø)
src/goto-instrument/race_check.cpp	0.00% <0.00%> (ø)
.../goto-instrument/synthesizer/synthesizer_utils.cpp	92.85% <ø> (-0.17%)	⬇️
src/goto-instrument/thread_instrumentation.cpp	0.00% <0.00%> (ø)
src/goto-instrument/undefined_functions.cpp	0.00% <0.00%> (ø)
src/goto-programs/string_instrumentation.cpp	25.11% <0.00%> (ø)
src/goto-instrument/accelerate/scratch_program.cpp	50.00% <33.33%> (-0.52%)	⬇️
src/goto-programs/builtin_functions.cpp	58.52% <78.72%> (+0.16%)	⬆️
src/ansi-c/goto_check_c.cpp	91.54% <80.95%> (-0.19%)	⬇️
src/goto-programs/string_abstraction.cpp	92.22% <97.56%> (-0.26%)	⬇️
... and 39 more

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