[turbofan] Introduce TruncateTaggedToWord32 simplified operator.

src/compiler/change-lowering.h

Index: src/compiler/change-lowering.h
diff --git a/src/compiler/change-lowering.h b/src/compiler/change-lowering.h
index 96590455efe6b806270454a02d5b150a18a90f07..ff3674f65eb0dba47e1327aff9a64e4d61ca3374 100644
--- a/src/compiler/change-lowering.h
+++ b/src/compiler/change-lowering.h
@@ -51,6 +51,7 @@ class ChangeLowering final : public Reducer {
   Reduction ChangeTaggedToUI32(Node* value, Node* control,
                                Signedness signedness);
   Reduction ChangeUint32ToTagged(Node* value, Node* control);
+  Reduction TruncateTaggedToWord32(Node* value, Node* control);
 
   Reduction LoadField(Node* node);
   Reduction StoreField(Node* node);