Improve documentation of QStringView::compare

Unify the documentation of QString::compare and QStringView::compare result. They mean the same but are written differently. QString doc is easier to understand IMO.

QString:

int QString::compare(const QString &s1, const QString &s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.

QStringView

int QStringView::compare(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns an integer that compares to zero as this string view compares to the string view str.