Use QStringList::join(QChar) overload where applicable [QtCore]

Use QStringList::join(QChar) overload where applicable [QtCore]

This is an automated change performing the following replacements:
                    join\("(.)"\) -> join('\1')
  join\(QLatin1String\("(.)"\)\)  -> join(QLatin1Char('\1'))
  join\(QStringLiteral\("(.)"\)\) -> join(QLatin1Char('\1'))

Change-Id: I81c378ef6aeeada5e116f1394cc9fc67f901ffd6
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>