QmlJS: Fix crash when opening JS files.

Now that Contexts are cached, it needs to be copyable. However, the
ScopeChain has a QmlComponentChain member that owns resources and didn't
have a correct copy constructor or copy assignment operator.

I've made QmlComponentChain non-copyable and store a shared pointer to
an instance instead, as it will generally not change for a given
context.

Reviewed-by: Lasse Holmstedt

src/libs/qmljs/qmljsinterpreter.h

@@ -242,8 +242,10 @@ class QMLJS_EXPORT ScopeChain
 public:
     ScopeChain();
 
-    struct QmlComponentChain
+    class QmlComponentChain
     {
+        Q_DISABLE_COPY(QmlComponentChain)
+    public:
         QmlComponentChain();
         ~QmlComponentChain();
 
@@ -255,7 +257,7 @@ public:
     };
 
     const ObjectValue *globalScope;
-    QmlComponentChain qmlComponentScope;
+    QSharedPointer<QmlComponentChain> qmlComponentScope;
     QList<const ObjectValue *> qmlScopeObjects;
     const ObjectValue *qmlTypes;
     QList<const ObjectValue *> jsScopes;