fix: std::char_traits is deprecated for other type than char

[Clement-Devevey]

Issue was the following:

`jniNativeLibrary.cpp:314:57: warning: 'char_traits' is deprecated: char_traits for T not equal to char, wchar_t, char8_t, char16_t or char32_t is non-standard and is provided for a temporary period. It will be removed in LLVM 18, so please migrate off of it. [-Wdeprecated-declarations]
return JavaCPP_createStringFromUTF16(env, ptr, std::char_traits::length(ptr));
^
char_traits.h:79:8: note: 'char_traits' has been explicitly marked deprecated here
struct LIBCPP_DEPRECATED("char_traits for T not equal to char, wchar_t, char8_t, char16_t or char32_t is non-standard and is provided for a temporary period. It will be removed in LLVM 18, so please migrate off of it.")
^
c++/v1/__config:772:53: note: expanded from macro 'LIBCPP_DEPRECATED'

define LIBCPP_DEPRECATED(m) attribute((deprecated(m)))`

[Clement-Devevey]

Or
return JavaCPP_createStringFromUTF16(env, ptr, std::char_traits<char16_t>::length(reinterpret_cast<const char16_t*>(ptr)));
not sure what's best

[saudet]

That doesn't sound like a correct fix. We need to know the length of the string in UTF-16.

char16_t is only available since C++11, so we need to use something else.

[saudet]

Maybe we could just put an ifdef else endif in there that uses char16_t for C++11 compilers and keep using unsigned short if not?