Deprecate multi-argument variants of exprt::copy_to_operands

[tautschnig]

add_to_operands or constructors with move semantics are preferable. All
existing uses of the newly deprecated methods have been reworked to use
non-deprecated methods.

Fixes: #2809

• 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

Merging #6671 (8dde888) into develop (1154f13) will increase coverage by 0.17%.
The diff coverage is 87.01%.

@@             Coverage Diff             @@
##           develop    #6671      +/-   ##
===========================================
+ Coverage    76.92%   77.10%   +0.17%     
===========================================
  Files         1583     1582       -1     
  Lines       183314   182609     -705     
===========================================
- Hits        141018   140799     -219     
+ Misses       42296    41810     -486     

Impacted Files	Coverage Δ
src/cpp/cpp_typecheck_conversions.cpp	85.14% <0.00%> (+0.10%)	⬆️
src/goto-instrument/dump_c.cpp	80.49% <0.00%> (+0.28%)	⬆️
src/goto-instrument/dump_c_class.h	100.00% <ø> (ø)
src/goto-instrument/goto_program2code.cpp	68.84% <0.00%> (+0.06%)	⬆️
src/goto-programs/builtin_functions.cpp	56.86% <0.00%> (ø)
src/goto-programs/xml_expr.cpp	51.21% <0.00%> (ø)
src/jsil/jsil_convert.cpp	0.00% <0.00%> (ø)
src/util/expr.h	96.96% <ø> (-0.26%)	⬇️
src/util/expr_util.h	100.00% <ø> (ø)
src/util/pointer_predicates.cpp	93.10% <ø> (-0.45%)	⬇️
... and 40 more

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