Complete Q*StringView literals

Following QTBUG-123851, we need literals for QUtf8StringView and QByteArrayView, too.

We should also add them for QASV, needs a different suffix, though, and the use of the QASV one should guarantee that L1 detection is done at compile-time (not like QTBUG-101014, which is only taking affect when assigning the QASV to a constexpr variable).

Open questions:

• what is ""_sv? A QByteArrayView or a QUtf8StringView (u8""_sv should be the latter, of course, so C++17/20 compat suggests that it be a QUtf8StringView). So ""_bav for QByteArrayView?
• what is the name of the UDLs for QAnyStringView? If C++ had template <char...> auto operator""_sv we could check in there for US-ASCII and return L1 or U8, depending on encoding, but that operator is only available for float/int literals; could maybe play tricks with passing the string as a non-type template argument, but that's probably C++20? Looks like we need _asv?