Use QString::compare(QStringView, Qt::CaseSensitivity) (#965)

Use QString::compare(QStringView, Qt::CaseSensitivity)  (#965)

* use QString::compare(QString, Qt::CaseSensitivity)

instead of case_ignore_strcmp with a QString and a character
literal.

* use QString::compare(QStringView, Qt::CaseSensitivity)

instead of QString::compare(QLatin1String, Qt::CaseSensitivity).

* compare QStrings to character literals instead of string literals that only contain one character.