syntax: add support for C++11 string literals - #4255

const char* raw_multiline = R"(
    This is a multiline raw string.
    " does not close the string.
    Escapes are not interpreted: \n \t \"
)";

// String literals: wide
const wchar_t* wide = L"Wide string";
const wchar_t* wide_raw = LR"(Wide "raw" string)";
const wchar_t* wide_escaped = L"Wide \u03A9 string";

// String literals: UTF-8
const char8_t* utf8 = u8"UTF-8 string";
const char8_t* utf8_raw = u8R"(UTF-8 "raw" string)";
const char8_t* utf8_unicode = u8"Hello, 世界!";

// String literals: UTF-16
const char16_t* utf16 = u"UTF-16 string";
const char16_t* utf16_raw = uR"(UTF-16 "raw" string)";
const char16_t* utf16_unicode = u"\u03A9";

// String literals: UTF-32
const char32_t* utf32 = U"UTF-32 string";
const char32_t* utf32_raw = UR"(UTF-32 "raw" string)";
const char32_t* utf32_unicode = U"\U0001F600";