AutoTest: Store referencing file inside test tree item

This duplicates (temporarily) the information for referencing files,
but the cache inside the parser will be removed within a later patch.

Change-Id: I7377864547f0d9ce074fa409b9c12067c4329d40
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>

src/plugins/autotest/testtreemodel.h

@@ -78,6 +78,8 @@ public:
     QMultiMap<QString, int> gtestNamesAndSets() const;
 #endif
 
+    QMap<QString, QString> referencingFiles() const;
+
 signals:
     void testTreeModelChanged();