QmlJS: Allow QML plugins to ship pre-dumped type descriptions.

If there's a library.xml file next to the qmldir file, Creator will
read that instead of trying to run qmldump on the library.

Reviewed-by: Erik Verbruggen

src/plugins/qmljstools/qmljsplugindumper.h

@@ -72,6 +72,9 @@ private:
         QString qmldirPath;
         QString importPath;
         QString importUri;
+
+        bool hasPredumpedXmlFile() const;
+        QString predumpedXmlFilePath() const;
     };
 
     void dump(const Plugin &plugin);