sketch: diff commenting: avoid re-sending old messages

When I was adding diff comments, it was sending me back to the chat
screen, which isn't what I wanted, since I want to send multiple
comments in one go. Furthermore, it was re-sending old comments
because of some new-to-me attribute stuff.

Finally I moved the comment box out of its right-hand corner to
the line I'm commenting on. (Sketch did this part.)

Co-Authored-By: sketch
diff --git a/loop/webui/src/web-components/sketch-chat-input.ts b/loop/webui/src/web-components/sketch-chat-input.ts
index fe14688..817190e 100644
--- a/loop/webui/src/web-components/sketch-chat-input.ts
+++ b/loop/webui/src/web-components/sketch-chat-input.ts
@@ -120,7 +120,9 @@
       composed: true,
     });
     this.dispatchEvent(event);
-    this.content = ""; // Clear the input after sending
+    // Clear the input after sending
+    this.content = "";
+    this.setAttribute("content", "");
   }
 
   adjustChatSpacing() {