CppTools: Use only const pointers for ProjectInfo and ProjectPart

All members were already const, but this makes it clear at all points of
use that these data structures are immutable.

Change-Id: Iea615c090bde462c445d15223caccc561b0c713d
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/autotest/loadprojectscenario.cpp

@@ -92,7 +92,8 @@ bool LoadProjectScenario::loadProject()
 
     CppTools::Tests::ProjectOpenerAndCloser projectManager;
     // This code must trigger a call to PluginManager::finishScenario() at some later point.
-    const CppTools::ProjectInfo::Ptr projectInfo = projectManager.open(projectFilePath, true, m_kit);
+    const CppTools::ProjectInfo::ConstPtr projectInfo = projectManager.open(projectFilePath,
+                                                                            true, m_kit);
     return projectInfo.get();
 }