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.cpp

@@ -39,7 +39,7 @@ namespace ClangCodeModel {
 namespace Internal {
 
 void RefactoringEngine::startLocalRenaming(const CppTools::CursorInEditor &data,
-                                           CppTools::ProjectPart *,
+                                           const CppTools::ProjectPart *,
                                            RenameCallback &&renameSymbolsCallback)
 {
     ClangdClient * const client