fix: Profiler doesn't handle UTF-8 files with BOM correctly.

[jaffinito]

Description

There was a regression caused by another fix, #3172, for handling wide characters properly. This swaps from wchar_t to xchar_t, which handles the differences better.

This was tested on ubuntu, fedora, alpine, and Windows with newrelic.config files and custom instrumentation files contain with a BOM and non-english characters (Japanese).

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed
• Performance testing completed with satisfactory results (if required)

Reviewer Checklist

• Perform code review
• Pull request was adequately tested (new/existing tests, performance tests)

[nrcventura]

Should we add a regression test for this?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.35%. Comparing base (3430d26) to head (3495c54).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3347      +/-   ##
==========================================
+ Coverage   82.33%   82.35%   +0.02%     
==========================================
  Files         495      495              
  Lines       32094    32094              
  Branches     3736     3736              
==========================================
+ Hits        26423    26430       +7     
+ Misses       4796     4790       -6     
+ Partials      875      874       -1     

Flag	Coverage Δ
Agent	83.58% <ø> (+0.02%)	⬆️
Profiler	70.40% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/Agent/NewRelic/Profiler/Common/FileUtils.h	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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