This PR introduces the new C++ methods `Term TermManager::mkString(const
std::u32string& s)` and `std::u32string Term::getU32StringValue()` to
replace old methods `Term TermManager::mkString(const std::wstring& s)`
and `std::wstring Term::getStringValue()`.
The reason for this change is that `wchar_t` has a platform-dependent
size: on Windows, it is 16-bit (UTF-16), while on Linux and macOS, it is
32-bit (UTF-32). However, the current implementation assumes that
`wchar_t` is always 32 bits. In contrast, `char32_t` and
`std::u32string` are explicitly designed for Unicode and have consistent
32-bit size across platforms.
Similarly, this PR also introduces C functions
`cvc5_mk_string_from_char32` and `cvc5_term_get_u32string_value`
to replace old functions `cvc5_mk_string_from_wchar` and
`cvc5_term_get_string_value`.
Although `char32_t` is part of the C11 standard, the `<uchar.h>` header
(which should define `char32_t`) is missing in Apple Clang. Therefore,
we explicitly provide a definition in such cases.
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Co-authored-by: Aina Niemetz <aina.niemetz@gmail.com>
