Added lexical editor feature flag

no issue

- adds `lexicalEditor` alpha labs flag and associated toggle in Admin
- when feature flag is enabled the new post/page routes will load the lexical editor instead of the mobiledoc editor

ghost/admin/app/routes/editor/new.js

@@ -1,6 +1,18 @@
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
+import {inject as service} from '@ember/service';
 
 export default class NewRoute extends AuthenticatedRoute {
+    @service feature;
+    @service router;
+
+    beforeModel(transition) {
+        super.beforeModel(...arguments);
+
+        if (this.feature.lexicalEditor) {
+            return this.transitionTo('lexical-editor.new', transition.to.params.type);
+        }
+    }
+
     model(params, transition) {
         let {type: modelName} = params;
 
@@ -13,7 +25,7 @@ export default class NewRoute extends AuthenticatedRoute {
     }
 
     // there's no specific controller for this route, instead all editor
-    // handling is done on the editor route/controler
+    // handling is done on the editor route/controller
     setupController(controller, newPost) {
         let editor = this.controllerFor('editor');
         editor.setPost(newPost);

ghost/admin/app/services/feature.js

@@ -66,6 +66,7 @@ export default class FeatureService extends Service {
     @feature('emailAlerts') emailAlerts;
     @feature('emailClicks') emailClicks;
     @feature('sourceAttribution') sourceAttribution;
+    @feature('lexicalEditor') lexicalEditor;
 
     _user = null;
 

ghost/admin/app/templates/settings/labs.hbs

@@ -265,6 +265,19 @@
                         </div>
                     </div>
                 </div>
+                <div class="gh-expandable-block">
+                    <div class="gh-expandable-header">
+                        <div>
+                            <h4 class="gh-expandable-title">Lexical editor</h4>
+                            <p class="gh-expandable-description">
+                               Makes lexical editor the default when creating new posts/pages.
+                            </p>
+                        </div>
+                        <div class="for-switch">
+                           <GhFeatureFlag @flag="lexicalEditor" />
+                        </div>
+                    </div>
+                </div>
             </div>
         </div>
         {{/if}}

ghost/core/core/shared/labs.js

@@ -33,7 +33,8 @@ const ALPHA_FEATURES = [
     'urlCache',
     'beforeAfterCard',
     'emailClicks',
-    'sourceAttribution'
+    'sourceAttribution',
+    'lexicalEditor'
 ];
 
 module.exports.GA_KEYS = [...GA_FEATURES];