This patch was generated by running:

```
perl -p -i \
     -e 's/^(\s+)([a-zA-Z0-9.]+) = NS_ConvertUTF8toUTF16\((.*)\);/\1CopyUTF8toUTF16(\3, \2);/;' \
     -e 's/^(\s+)([a-zA-Z0-9.]+) = NS_ConvertUTF16toUTF8\((.*)\);/\1CopyUTF16toUTF8(\3, \2);/;' \
     $FILE
```

against every .cpp and .h in mozilla-central, and then fixing up the
inevitable errors that happen as a result of matching C++ expressions with
regexes.  The errors fell into three categories:

1. Calling the convert functions with `std::string::c_str()`; these were
   changed to simply pass the string instead, relying on implicit conversion
   to `mozilla::Span`.
2. Calling the convert functions with raw pointers, which is not permitted
   with the copy functions; these were changed to invoke `MakeStringSpan` first.
3. Other miscellaneous errors resulting from over-eager regexes and/or the
   replacement not being type-aware.  These changes were reverted.

Differential Revision: https://phabricator.services.mozilla.com/D88903