Add mobile_embed to Discussion Edit/Create view

flag=none
closes VICE-2967

test plan:
  - Tests pass
  - Go to /courses/[Course ID]/discussion_topics/[Discussion ID]/edit?embed=true
  - Shouldn't have the navigation bar and other surrounding things
      around the Discussion Edit/Create view.
  - The published/not published thing should appear on top right and adjust
      accordingly.

qa risk: low

Change-Id: I02ce835824c4035230946b88598956569c7c1977
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/298467
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jason Gillett <jason.gillett@instructure.com>
Product-Review: Jason Gillett <jason.gillett@instructure.com>
QA-Review: Chawn Neal <chawn.neal@instructure.com>

app/controllers/discussion_topics_controller.rb

@@ -662,7 +662,7 @@ class DiscussionTopicsController < ApplicationController
 
     set_master_course_js_env_data(@topic, @context)
     conditional_release_js_env(@topic.assignment)
-    render :edit
+    render :edit, layout: params[:embed] == "true" ? "mobile_embed" : true
   end
 
   def show
@@ -774,9 +774,12 @@ class DiscussionTopicsController < ApplicationController
         end
       end
 
+      edit_url = context_url(@topic.context, :edit_context_discussion_topic_url, @topic)
+      edit_url += "?embed=true" if params[:embed] == "true"
+
       js_env({
                course_id: params[:course_id] || @context.course&.id,
-               EDIT_URL: context_url(@topic.context, :edit_context_discussion_topic_url, @topic),
+               EDIT_URL: edit_url,
                PEER_REVIEWS_URL: @topic.assignment ? context_url(@topic.assignment.context, :context_assignment_peer_reviews_url, @topic.assignment.id) : nil,
                discussion_topic_id: params[:id],
                manual_mark_as_read: @current_user&.manual_mark_as_read?,

app/stylesheets/bundles/discussions_edit.scss

@@ -39,3 +39,7 @@
 label.short-label {
   display: inline-block;
 }
+
+.full-width {
+  width: 100%;
+}

ui/features/discussion_topic_edit/backbone/views/EditView.coffee

@@ -139,7 +139,12 @@ export default class EditView extends ValidatedFormView
     if returnToHelper.isValid(params['return_to'])
       params['return_to']
     else
-      @model.get 'html_url'
+      url = new URL(window.location.href)
+      searchParams = new URLSearchParams(url.search)
+      if searchParams.get('embed') == 'true'
+        (@model.get 'html_url') + "?embed=true"
+      else
+        @model.get 'html_url'
 
   redirectAfterCancel: ->
     location = @locationAfterCancel(deparam())

ui/features/discussion_topic_edit/jst/EditView.handlebars

@@ -21,7 +21,7 @@
       {{> ui/features/discussion_topic_edit/jst/_publishedButton.handlebars }}
     </ul>
     {{else}}
-    <div class="span4 offset8 text-right">
+    <div class="full-width text-right">
       {{> ui/features/discussion_topic_edit/jst/_publishedButton.handlebars }}
     </div>
   </div>
@@ -378,4 +378,4 @@
   {{/if}}
   <button type="submit" data-text-while-loading="{{#t " saving"}}Saving...{{/t}}" class="btn btn-primary">{{#t
     "save"}}Save{{/t}}</button>
-</div>
+</div>