FIX: Update post's raw from server response (#13438)

This fix is similar to ea2833d0d8, but
this time raw text is updated after the post is created.

app/serializers/new_post_result_serializer.rb

@@ -13,7 +13,7 @@ class NewPostResultSerializer < ApplicationSerializer
   has_one :pending_post, serializer: TopicPendingPostSerializer, root: false, embed: :objects
 
   def post
-    post_serializer = PostSerializer.new(object.post, scope: scope, root: false)
+    post_serializer = PostSerializer.new(object.post, scope: scope, root: false, add_raw: true)
     post_serializer.draft_sequence = DraftSequence.current(scope.user, object.post.topic.draft_key)
     post_serializer.as_json
   end

spec/requests/api/schemas/json/topic_create_response.json

@@ -19,6 +19,9 @@
     "created_at": {
       "type": "string"
     },
+    "raw": {
+      "type": "string"
+    },
     "cooked": {
       "type": "string"
     },

spec/requests/posts_controller_spec.rb

@@ -997,6 +997,7 @@ describe PostsController do
         expect(response.status).to eq(200)
         parsed = response.parsed_body
         expect(parsed['post']).to be_present
+        expect(parsed['post']['raw']).to eq('this is the test content')
         expect(parsed['post']['cooked']).to be_present
       end