textproc/zxing-cpp: fix build with libc++ 19
As noted in the libc++ 19 release notes [1], std::char_traits<> is now
only provided for char, char8_t, char16_t, char32_t and wchar_t, and any
instantiation for other types will fail.
This causes textproc/zxing-cpp to fail to compile with clang 19 and
libc++ 19, resulting in errors similar to:
/usr/include/c++/v1/string_view:300:42: error: implicit instantiation of undefined template 'std::char_traits<unsigned char>'
300 | static_assert(is_same<_CharT, typename traits_type::char_type>::value,
| ^
/wrkdirs/usr/ports/textproc/zxing-cpp/work/zxing-cpp-2.2.1/core/src/Utf.cpp:72:42: note: in instantiation of template class 'std::basic_string_view<unsigned char>' requested here
72 | static size_t Utf8CountCodePoints(utf8_t utf8)
| ^
/usr/include/c++/v1/__string/char_traits.h:45:8: note: template is declared here
45 | struct char_traits;
| ^utf8_t is effectively defined as std::basic_string<uint8_t>, which
is no longer possible. So redefine it as a std::vector<uint8_t>
instead.
This requires only a small adjustment in one other place: replacing the
initializer list in the AppendFromUtf8 call in FromUtf8.
[1] https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals
PR: 280791
Approved by: tcberner (maintainer)
MFH: 2024Q3