FEATURE: Update the topic excerpt when the OP is rebaked (#9852)

* We now have a site setting "topic_excerpt_maxlength" that is used when the OP is created or revised to generate a topic excerpt.
* However, posts created before this setting was introduced cannot benefit from this change unless they are revised, and if the topic excerpt length setting is changed that situation is also not covererd.
* This PR makes a change to rebake! to update the topic excerpt IF the post is the OP.

spec/models/post_spec.rb

@@ -1195,6 +1195,25 @@ describe Post do
       expect(post.cooked).to eq(first_cooked)
       expect(result).to eq(true)
     end
+
+    it "updates the topic excerpt at the same time if it is the OP" do
+      post = create_post
+      post.topic.update(excerpt: "test")
+      DB.exec("UPDATE posts SET cooked = 'frogs' WHERE id = ?", [ post.id ])
+      post.reload
+      result = post.rebake!
+      post.topic.reload
+      expect(post.topic.excerpt).not_to eq("test")
+    end
+
+    it "does not update the topic excerpt if the post is not the OP" do
+      post = create_post
+      post2 = create_post
+      post.topic.update(excerpt: "test")
+      result = post2.rebake!
+      post.topic.reload
+      expect(post.topic.excerpt).to eq("test")
+    end
   end
 
   describe "#set_owner" do