introduce code_frontend_declt

[kroening]

This introduces code_fontend_declt, which separates code_declt (for use in goto instructions) and the statement in C programs.

The two differ (the variant for goto programs has no initializer), and separating them enables changes.

• Each commit message has a non-empty body, explaining why the change was made.
• 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).
• 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 #6387 (7649e74) into develop (af94148) will increase coverage by 0.00%.
The diff coverage is 83.67%.

@@           Coverage Diff            @@
##           develop    #6387   +/-   ##
========================================
  Coverage    75.97%   75.98%           
========================================
  Files         1523     1523           
  Lines       164191   164209   +18     
========================================
+ Hits        124748   124767   +19     
+ Misses       39443    39442    -1     

Impacted Files	Coverage Δ
src/ansi-c/expr2c_class.h	100.00% <ø> (ø)
src/goto-instrument/dot.cpp	0.00% <0.00%> (ø)
src/goto-programs/goto_convert_class.h	87.30% <ø> (ø)
src/goto-programs/goto_program.h	90.43% <ø> (+0.15%)	⬆️
src/jsil/jsil_convert.cpp	0.00% <0.00%> (ø)
src/cpp/cpp_typecheck_code.cpp	80.70% <40.00%> (ø)
src/goto-instrument/dump_c.cpp	79.59% <50.00%> (ø)
src/cpp/parse.cpp	68.61% <57.14%> (ø)
src/goto-symex/symex_main.cpp	86.00% <60.00%> (+0.03%)	⬆️
src/goto-analyzer/taint_analysis.cpp	78.21% <75.00%> (-0.22%)	⬇️
... and 15 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 038a53b...7649e74. Read the comment docs.

[peterschrammel]

What is the next step after this? Is it to remove deprecated uses of code_Xt in goto programs?

[kroening]

yes, the goal is to remove the use of codet in goto-programs.

[peterschrammel]

Would it make sense to keep the name code_declt for the frontend occurrences that will be kept in the end and rename the deprecated uses in goto-program?

[kroening]

This is to be consistent with frontend_pointer.