Fix issue with closing comment

While we typically want to use new objects, so that lit knows that
something has changed. This breaks for messages, as we need the original
message in the model to store whether it is expanded or not, otherwise
when a comment is saved and gr-comment-messages is retriggered to
render, the messages have all expanded set to false again.

Google-Bug-Id: b/232286621
Release-Notes: skip
Change-Id: Id116e2b4d2c86e0890bb2635571ec4507048a4e3
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
index 65e42a1..0902fe6 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
@@ -663,7 +663,8 @@
       return;
     }
     e.stopPropagation();
-    this.message = {...this.message, expanded: true};
+    this.message.expanded = true;
+    this.requestUpdate();
   }
 
   private handleAuthorClick(e: Event) {
@@ -671,7 +672,8 @@
       return;
     }
     e.stopPropagation();
-    this.message = {...this.message, expanded: false};
+    this.message.expanded = false;
+    this.requestUpdate();
   }
 
   // private but used in tests.
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
index c03121d..f6b0ad4 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.ts
@@ -324,7 +324,8 @@
       return;
     }
 
-    el.message = {...el.message, expanded: true};
+    el.message.expanded = true;
+    el.requestUpdate();
     await el.updateComplete;
     let top = el.offsetTop;
     for (