CMake: Pass const QList<const FileNode *> to Directory Readers

This makes sure they need to copy whatever they need.

Change-Id: I767ac0c5f54ca1f9f46acdefe4bd7fea35657312
Reviewed-by: Alexander Drozdov <adrozdoff@gmail.com>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cmakeprojectmanager/cmakeproject.cpp

@@ -392,7 +392,7 @@ void CMakeProject::handleParsingStarted()
 void CMakeProject::handleTreeScanningFinished()
 {
     qDeleteAll(m_allFiles);
-    m_allFiles = m_treeScanner.release();
+    m_allFiles = Utils::transform(m_treeScanner.release(), [](const FileNode *fn) { return fn; });
 
     auto t = activeTarget();
     if (!t)