QmlJS: Fix checking for case and default blocks

case and default blocks inside a switch statement are just
special statement lists which need proper handling to avoid
wrong warnings regarding using standalone blocks.

Task-number: QTCREATORBUG-24214
Change-Id: Ia682b13ed4df21c5831308193d5abaf5163bde59
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/libs/qmljs/qmljscheck.h

@@ -122,6 +122,8 @@ private:
     bool isQtQuick2() const;
     bool isQtQuick2Ui() const;
 
+    bool isCaseOrDefault(AST::Node *n);
+
     AST::Node *parent(int distance = 0);
 
     Document::Ptr _doc;