String View Additions

When using QStringView, I sometimes miss functionality/shorthands that I know from other languages/libraries. While it's not impossible to emulate them with the current API, it hides a bit of intent when reading the code. This applies to all string view types, but I'm using QStringView as the example.

• Remove a matching part from the beginning or end. LLVM: consume_front/back, Rust: strip_prefix/suffix, Python: remove_prefix/suffix
  I'm not sure what the ideal signature would be here. Having the ability to do chaining would be nice. So maybe stripPrefix(T prefix, Qt::CaseSensitivity cs = insensitive, bool *ok = nullptr) -> QStringView&?
• Split a string into exactly two parts. LLVM: split, Rust: split_once
  This is particularly useful when you know that there will only be two parts. I think the behavior of LLVM would be nice in that it always returns a pair.

A bit related to https://bugreports.qt.io/browse/QTBUG-115007: having toLower(), toUpper(), and replace() could make code more concise. This hides the allocation for a QString a bit, but avoiding the intermediate .toString() seems worthy.