CMakePM: Scan files only on CMake configuration failure

The file tree scanner will only be started on CMake configuration
failure to generate the <File System> fall back project node.

Change-Id: I873ef1189fd43dc9bffa03aeafabb00bb3b8b6af
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/fileapireader.h

@@ -71,8 +71,6 @@ public:
     QList<CMakeBuildTarget> takeBuildTargets(QString &errorMessage);
     CMakeConfig takeParsedConfiguration(QString &errorMessage);
     QString ctestPath() const;
-    std::unique_ptr<CMakeProjectNode> generateProjectTree(
-        const ProjectExplorer::TreeScanner::Result &allFiles, bool failedToParse);
     ProjectExplorer::RawProjectParts createRawProjectParts(QString &errorMessage);
 
     bool isMultiConfig() const;
@@ -80,6 +78,10 @@ public:
 
     int lastCMakeExitCode() const;
 
+    std::unique_ptr<CMakeProjectNode> rootProjectNode();
+
+    Utils::FilePath topCmakeFile() const;
+
 signals:
     void configurationStarted() const;
     void dataAvailable(bool restoredFromBackup) const;