Fix #4987: Can't populate tag string from upload url anymore.

Usage: https://danbooru.donmai.us/uploads/new?url=...&post[tag_string]=...&post[rating]=...

* Pass the URL parameters from the /uploads/new page to the /uploads/:id page.
* Fix the /uploads/:id page throwing an "unpermitted parameters" error
  when given URL params for the post edit form.

test/functional/uploads_controller_test.rb

@@ -138,6 +138,14 @@ class UploadsControllerTest < ActionDispatch::IntegrationTest
 
         assert_redirected_to @post
       end
+
+      should "prefill the upload form with the URL parameters" do
+        upload = create(:completed_source_upload, uploader: @user)
+        get_auth upload_path(upload, post: { rating: "s" }), @user
+
+        assert_response :success
+        assert_select "#post_rating_s[checked]"
+      end
     end
 
     context "create action" do