Update replaceUnicode() to handle two \U{} calls in a row.

[dpvc]

This PR fixes an issue with the string utility's replaceUnicode() function that prevented it from processing two adjacent \U{} calls, so replaceUnicode('\U{A0}\U{A0}') would only replace the first \U, not the second. That was due to the requirement of having a non-\ character preceding the \U which blocked it from matching the second \U, as that character can't be part of a previous replacement. That requirement was part of an attempt to avoid escaped backslashes like \\U. But, in addition to the problem it caused for replacing the \U{}, the escaped backslashes were never converted to single backslashes. The new code now properly does that as well.

The tests are adjusted to accommodate the translation of \\ to \, and to add a pair of adjacent \U.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.71%. Comparing base (e68c42f) to head (ad0ab7e).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1322   +/-   ##
========================================
  Coverage    86.71%   86.71%           
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  Files          337      337           
  Lines        84074    84075    +1     
  Branches      4758     4759    +1     
========================================
+ Hits         72904    72905    +1     
+ Misses       11170    11147   -23     
- Partials         0       23   +23     

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[zorkow]

lgtm.