QItemDelegate: Use QString::replace instead of home brew algorithm

Change-Id: I491b6167147de48bd3be2aaf616c9dad43dabebb
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/widgets/itemviews/qitemdelegate.cpp

@@ -94,10 +94,7 @@ public:
 
     inline static QString replaceNewLine(QString text)
         {
-            const QChar nl = QLatin1Char('\n');
-            for (int i = 0; i < text.count(); ++i)
-                if (text.at(i) == nl)
-                    text[i] = QChar::LineSeparator;
+            text.replace(QLatin1Char('\n'), QChar::LineSeparator);
             return text;
         }