DEV: Add post_id parameter to reset_bump_date route (#25372)

This would allow a theme component (or an API call) to reset the bump
date of a topic to a given post's created_at date.

I picked `post_id` as the parameter here because it provides a bit of
extra protection against accidentally resetting the bump date to a date
that doesn't make sense.

app/controllers/topics_controller.rb

@@ -1151,12 +1151,14 @@ class TopicsController < ApplicationController
 
   def reset_bump_date
     params.require(:id)
+    params.permit(:post_id)
+
     guardian.ensure_can_update_bumped_at!
 
     topic = Topic.find_by(id: params[:id])
     raise Discourse::NotFound.new unless topic
 
-    topic.reset_bumped_at
+    topic.reset_bumped_at(params[:post_id])
     render body: nil
   end
 

app/models/topic.rb

@@ -1858,13 +1858,21 @@ class Topic < ActiveRecord::Base
     @is_category_topic ||= Category.exists?(topic_id: self.id.to_i)
   end
 
-  def reset_bumped_at
+  def reset_bumped_at(post_id = nil)
     post =
-      ordered_posts.where(
-        user_deleted: false,
-        hidden: false,
-        post_type: Post.types[:regular],
-      ).last || first_post
+      (
+        if post_id
+          Post.find_by(id: post_id)
+        else
+          ordered_posts.where(
+            user_deleted: false,
+            hidden: false,
+            post_type: Post.types[:regular],
+          ).last || first_post
+        end
+      )
+
+    return if !post
 
     self.bumped_at = post.created_at
     self.save(validate: false)