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

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

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

Change-Id: Ia087beb886bbaec1a0976cd924440d8904044879
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>