[#3532] Replace Name::NameString with vector of uint8_t

[#3532] Replace Name::NameString with vector of uint8_t

As noted in the libc++ 19 release notes, it now only provides
std::char_traits<> for types char, char8_t, char16_t, char32_t and
wchar_t, and any instantiation for other types will fail.

Name::NameString is defined as a std::basic_string<uint8_t>, so that
will no longer work. Redefine it as a std::vector<uint8_t> instead.