[DI] Element refs on _storage should be printed with self.

`_storage` comes from `assign_by_wrapper` instruction but
user wrote `self.` in the source and that is what should
get printed by DI diagnostics.

Author: xedin

lib/SILOptimizer/Mandatory/DIMemoryUseCollector.cpp

@@ -413,7 +413,7 @@ DIMemoryObjectInfo::getPathStringToElement(unsigned Element,
                                            std::string &Result) const {
   auto &Module = MemoryInst->getModule();
 
-  if (isAnyInitSelf())
+  if (isAnyInitSelf() || getAsTypeWrapperLocalStorageVar())
     Result = "self";
   else if (ValueDecl *VD =
                dyn_cast_or_null<ValueDecl>(getLoc().getAsASTNode<Decl>()))