fix(accessibility): Add main and complimentary landmarks

Screen readers and other assistive technologies use it for navigation

Closes #15658

common/app/routes/challenges/views/classic/Editor.jsx

@@ -118,7 +118,10 @@ export class Editor extends PureComponent {
       mode
     } = this.props;
     return (
-      <div className={ `${ns}-editor` }>
+      <div
+        className={ `${ns}-editor` }
+        role='main'
+        >
         <NoSSR onSSR={ <CodeMirrorSkeleton content={ content } /> }>
           <Codemirror
             onChange={ classicEditorUpdated }

common/app/routes/challenges/views/classic/Side-Panel.jsx

@@ -127,6 +127,7 @@ export class SidePanel extends PureComponent {
       <div
         className={ `${ns}-instructions-panel` }
         ref='panel'
+        role='complementary'
         >
         <div>
           <ChallengeTitle>