QmlJS: Avoid an infinite loop if a qmltypes file has a cycle.

The qmltypes files shipped with libraries shouldn't, but could define
components that form a prototype cycle. Use of the new
QmlObjectValue::prototypes() function avoids the code model getting
stuck in an infinite loop for these cases.

For plain ObjectValues this is already solved by using
PrototypeIterator.

Change-Id: I0f562672ab99b454bc3a0121c7a1b9eca43476bb
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>

src/libs/qmljs/qmljsinterpreter.h

@@ -428,6 +428,7 @@ public:
 
     using ObjectValue::prototype;
     const QmlObjectValue *prototype() const;
+    QList<const QmlObjectValue *> prototypes() const;
 
     const QmlObjectValue *attachedType() const;
     void setAttachedType(QmlObjectValue *value);