QmlJS: Move ensuredGetDocumentForPath to ModelManagerInterface

The new function does properly update the latest snapshot.

Change-Id: If3148701e2f98c39a0822d1395b43f4fa7ee1949
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>

src/libs/qmljs/qmljsmodelmanagerinterface.h

@@ -199,6 +199,9 @@ public:
 
     // Blocks until all parsing threads are done. Used for testing.
     void joinAllThreads();
+
+    QmlJS::Document::Ptr ensuredGetDocumentForPath(const QString &filePath);
+
 public slots:
     virtual void resetCodeModel();
     void removeProjectInfo(ProjectExplorer::Project *project);