Allow characters with value >= 128 in XML output

[thomasspriggs]

These values are used as part of printable characters which should be allowed in XML output. This invariant was previously violated for characters such as ¬ and ⇔ which are included in the output when cbmc is invoked with --verbosity 10 --xml-ui. This was due to the comparison formerly being a signed comparison. So byte values in the range 128 to 255 were treated as values in the -128 to -1 range which are less than which has value 32.

This PR should address issue #7038

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[codecov]

Codecov Report

Merging #7109 (8691d65) into develop (e6fc280) will increase coverage by 0.04%.
The diff coverage is 94.91%.

@@             Coverage Diff             @@
##           develop    #7109      +/-   ##
===========================================
+ Coverage    77.87%   77.92%   +0.04%     
===========================================
  Files         1576     1576              
  Lines       181587   181611      +24     
===========================================
+ Hits        141412   141512     +100     
+ Misses       40175    40099      -76     

Impacted Files	Coverage Δ
src/cpp/cpp_template_type.h	52.94% <0.00%> (-11.35%)	⬇️
src/goto-instrument/dump_c.cpp	80.86% <0.00%> (ø)
src/goto-instrument/function.cpp	0.00% <0.00%> (ø)
src/util/xml.cpp	73.88% <ø> (ø)
src/ansi-c/c_typecheck_type.cpp	77.16% <86.66%> (+0.05%)	⬆️
.../src/java_bytecode/java_bytecode_convert_class.cpp	94.18% <100.00%> (+0.01%)	⬆️
...src/java_bytecode/java_bytecode_typecheck_type.cpp	96.00% <100.00%> (ø)
jbmc/src/java_bytecode/java_object_factory.cpp	94.40% <100.00%> (+0.02%)	⬆️
jbmc/src/java_bytecode/java_pointer_casts.cpp	92.50% <100.00%> (ø)
jbmc/src/java_bytecode/java_types.cpp	95.13% <100.00%> (+0.02%)	⬆️
... and 29 more

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