AutoTest: Use working copy of own parser

In TestCodeParser::syncTestFrameworks(), a parser is created for every
test framework. As a result, the last parser being created would "win"
the global s_parserInstance variable, which is not predictable and
probably not intended. So turn CppParser::getFileContent() into a non-
static method, avoiding the global variable altogether.

Change-Id: I9f7560f1185bc4a3bc7b2b36e89280351998465e
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/autotest/qtest/qttestparser.h

@@ -27,6 +27,10 @@
 
 #include "../itestparser.h"
 
+#include "qttesttreeitem.h"
+
+namespace CppTools { class CppModelManager; }
+
 namespace Autotest {
 namespace Internal {
 
@@ -52,6 +56,8 @@ public:
                          const QString &fileName) override;
 
 private:
+    QString testClass(const CppTools::CppModelManager *modelManager, const QString &fileName) const;
+    QHash<QString, QtTestCodeLocationList> checkForDataTags(const QString &fileName) const;
     QHash<QString, QString> m_testCaseNames;
     QMultiHash<QString, QString> m_alternativeFiles;
 };