Message handler: add quote_begin, quote_end commands

[tautschnig]

These will permit custom formatting of quoting for each message handler, and for a start introduce tags for XML. See #4875 for discussion.

Please review commit-by-commit.

• 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

❌ Patch coverage is 28.90625% with 91 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.38%. Comparing base (2e6200a) to head (476ebc2).

Files with missing lines	Patch %	Lines
src/util/ui_message.h	14.54%	47 Missing ⚠️
src/goto-analyzer/taint_parser.cpp	0.00%	16 Missing ⚠️
src/statement-list/statement_list_entry_point.cpp	0.00%	8 Missing ⚠️
src/ansi-c/c_typecheck_code.cpp	0.00%	4 Missing ⚠️
src/ansi-c/c_typecheck_base.cpp	0.00%	3 Missing ⚠️
src/solvers/strings/string_refinement.cpp	0.00%	3 Missing ⚠️
src/ansi-c/c_typecheck_expr.cpp	0.00%	2 Missing ⚠️
src/cpp/cpp_instantiate_template.cpp	0.00%	2 Missing ⚠️
src/cpp/cpp_typecheck_expr.cpp	0.00%	2 Missing ⚠️
src/cpp/cpp_typecheck_function.cpp	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5696      +/-   ##
===========================================
- Coverage    80.39%   80.38%   -0.02%     
===========================================
  Files         1688     1688              
  Lines       207403   207485      +82     
  Branches        73       73              
===========================================
+ Hits        166749   166781      +32     
- Misses       40654    40704      +50     

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[martin-cs]

Seems good. It would be nice if this also had the implementation of this for XML so that it was clear why it was valueable and no-one will accidentally 'simplify' it out.

[peterschrammel]

Not sure this is a good idea as it changes the XML output format. I'd stick to single quotes for now and introduce a different format in a separate PR if desired.

[tautschnig]

I have now factored this into a commit of its own, which could thus easily be dropped from the series.

[peterschrammel]

I would really prefer to drop this commit. IMO, it causes unnecessary hassle to XML output users.

[tautschnig]

Removed, just left behind a comment that this could be done.