QmlDesigner: Fix renaming materials

Check for id validity during id generation and try to fix invalid id.

Fixes: QDS-7437
Change-Id: I9d7665cbebdce8ee3395e4abe9ee14b26866f761
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/qmldesigner/designercore/model/model.cpp

@@ -1577,6 +1577,10 @@ QString Model::generateIdFromName(const QString &name, const QString &fallbackId
             newId.prepend('_');
     }
 
+    // If the new id is not valid (e.g. qml keyword match), try fixing it by prepending underscore
+    if (!ModelNode::isValidId(newId))
+        newId.prepend("_");
+
     QRegularExpression rgx("\\d+$"); // matches a number at the end of a string
     while (hasId(newId)) { // id exists
         QRegularExpressionMatch match = rgx.match(newId);