QmlJSEditor: cleanup updateOutlineIndexNow

It was called to often - it was already connected in setEditor method.
Change outlineModelIndex() to be just a getter and call the
updateOutlineIndexNow() where an update is necessary.

Change-Id: I6f30bfaff74237416c1aef5418860179c1f8ebf7
Reviewed-by: Marco Benelli <marco.benelli@qt.io>

src/plugins/qmljseditor/qmljseditor.h

@@ -66,6 +66,7 @@ public:
     QmlJSEditorDocument *qmlJsEditorDocument() const;
 
     QModelIndex outlineModelIndex();
+    void updateOutlineIndexNow();
 
     TextEditor::AssistInterface *createAssistInterface(TextEditor::AssistKind assistKind,
                            TextEditor::AssistReason reason) const override;
@@ -84,7 +85,6 @@ private:
     void modificationChanged(bool);
 
     void jumpToOutlineElement(int index);
-    void updateOutlineIndexNow();
     void updateContextPane();
     void showTextMarker();