[libc] Add iswctype and wctype (#191178)
Implement the iswctype and wctype functions from <wctype.h>.
- Add wctype_t type definition.
- Implement wctype to map property strings to classification
descriptors.
- Implement iswctype as a dispatcher over existing wide character
classification functions.
- Add corresponding entrypoints and unit tests.
Refs: https://github.com/llvm/llvm-project/issues/191076
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Co-authored-by: Zile Xiong <xiongzile99@gmail.com>
