Remove preprocessing of CProverString.insert for non-String arguments

[romainbrenguier]

We replace the preprocessing of CProverString.insert for characters, booleans etc. and provide models that use String.valueOf and the String version of CProverString.insert instead.
This is too reduce the number of builtin functions the solver has too handle, making it simpler and easier too debug and test, and less likely to have bugs, without reducing its expressive power: we can still get the same behavior as before by combining two function calls.

• Each commit message has a non-empty body, explaining why the change was made.
• [na] Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• 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).
• [na] My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov-io]

Codecov Report

Merging #5035 into develop will increase coverage by 0.01%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           develop    #5035      +/-   ##
===========================================
+ Coverage    69.53%   69.54%   +0.01%     
===========================================
  Files         1314     1314              
  Lines       108988   108921      -67     
===========================================
- Hits         75786    75751      -35     
+ Misses       33202    33170      -32

Impacted Files	Coverage Δ
...c/java_bytecode/java_string_library_preprocess.cpp	96.83% <ø> (-0.06%)	⬇️
...lvers/strings/string_constraint_generator_main.cpp	84.44% <ø> (+1.11%)	⬆️
src/solvers/strings/string_constraint_generator.h	100% <ø> (ø)	⬆️
...ers/strings/string_constraint_generator_insert.cpp	81.08% <0%> (+23.24%)	⬆️

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[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 0d71098).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/123717057

[allredj]

⚠️
This PR failed Diffblue compatibility checks (cbmc commit: ea21cca).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/123947553
Status will be re-evaluated on next push.
Common spurious failures include: the cbmc commit has disappeared in the mean time (e.g. in a force-push); the author is not in the list of contributors (e.g. first-time contributors); compatibility was already broken by an earlier merge.

[romainbrenguier]

the corresponding test-gen pull request passed CI https://github.com/diffblue/test-gen/pull/3806

[romainbrenguier]

java-models-library update now pointing to master

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 2402773).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/124071536