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/clangcodemodel/clangrefactoringengine.h

@@ -42,7 +42,7 @@ class RefactoringEngine : public CppTools::RefactoringEngineInterface
 {
 public:
     void startLocalRenaming(const CppTools::CursorInEditor &data,
-                            CppTools::ProjectPart *projectPart,
+                            const CppTools::ProjectPart *projectPart,
                             RenameCallback &&renameSymbolsCallback) override;
     void globalRename(const CppTools::CursorInEditor &cursor, CppTools::UsagesCallback &&callback,
                       const QString &replacement) override;