Use more QAnyStringView in our APIs

There are three target levels here, which should be tackled in order.

1. no-brainers like fromString() named (or normal) constructors, which never store the string
2. functions like JSON/CBOR/settings index operators, QRegularExpression, but also{{QPainter::drawText()}}, which do not primarily store the string, so don't participate in QString's implicit sharing
3. functions which primarily store a string