Autotest: extract cpp document lookup into cpp test parser

Change-Id: I261684206ec7ff9a97ca4a88b5846ebbc0fdda47
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/autotest/itestparser.h

@@ -81,6 +81,8 @@ public:
     static QByteArray getFileContent(const QString &filePath);
     void release() override;
 
+    CPlusPlus::Document::Ptr document(const QString &fileName);
+
 protected:
     CPlusPlus::Snapshot m_cppSnapshot;
     CppTools::WorkingCopy m_workingCopy;