qUtf8Printable() should work for QStringView and QStringRef

The following GoogleTest pretty printer does not compile:

inline void PrintTo(QStringView string, ::std::ostream *os)
{
  *os << qUtf8Printable(string);
}

One would expect qPrintable(), qUtf8Printable(), and qUtf16Printable() to work for all the Qt string classes.

The workaround is to explicitly call QStringView::toUtf8() etc instead.