introduce instructiont::call_function() and related methods

[kroening]

This completes the new API of goto_programt::instructiont by introducing methods for accessing the properties of function calls.

• 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/
• n/a 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

Merging #6281 (41e54d7) into develop (19947e9) will decrease coverage by 0.00%.
The diff coverage is 78.57%.

@@             Coverage Diff             @@
##           develop    #6281      +/-   ##
===========================================
- Coverage    75.90%   75.90%   -0.01%     
===========================================
  Files         1492     1492              
  Lines       162712   162705       -7     
===========================================
- Hits        123509   123503       -6     
+ Misses       39203    39202       -1     

Impacted Files	Coverage Δ
src/goto-instrument/contracts/contracts.cpp	92.59% <ø> (ø)
src/goto-programs/goto_program.cpp	68.48% <53.84%> (+0.08%)	⬆️
src/goto-programs/parameter_assignments.cpp	71.42% <60.00%> (-0.80%)	⬇️
src/goto-programs/goto_program.h	89.41% <66.66%> (-1.28%)	⬇️
src/goto-programs/interpreter.cpp	51.45% <72.72%> (+0.08%)	⬆️
src/analyses/constant_propagator.cpp	95.06% <85.71%> (+0.85%)	⬆️
src/goto-programs/cfg.h	85.36% <100.00%> (ø)
src/goto-programs/goto_inline_class.cpp	87.17% <100.00%> (-0.04%)	⬇️
src/goto-programs/instrument_preconditions.cpp	91.66% <100.00%> (ø)
...oto-programs/label_function_pointer_call_sites.cpp	100.00% <100.00%> (ø)
... and 4 more

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