Spike AXE A11Y testing in Cypress (#9111)

* Spike AXE A11Y testing in Cypress

* Fix NewRoomIntro breaking html/aria list rules

* Fix HeaderButtons breaking aria role semantics rules

* missing type

* Switch left panel from aside to nav and include space panel

* Give the page a main heading of the room name when viewing a room

* Use header landmark on RoomHeader

* Improve aria attributes on composer when autocomplete is closed

* Fix aria-owns on RoomHeader

* Give Spinner an aria role

* Give server picker help button an aria label

* Improve auth aria attributes and semantics

* Improve heading semantics in use case selection screen

* Fix autocomplete attribute to be valid

* Fix heading semantics on login page

* Improve Cypress axe testing

* Add axe tests

* Stop synapse after the timeline tests

* Await spinners to fade before percy snapshotting timeline tests

* Improve naming of plugin

* Update snapshots

* Fix accidental heading change

* Fix double synapse stoppage

* Fix Cypress timeline avatar assertions to be DPI agnostic

* Fix aria attributes on date separators

* delint

* Update snapshots

* Revert style change

* Skip redundant call

src/components/structures/LeftPanel.tsx

@@ -382,7 +382,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
 
         return (
             <div className={containerClasses}>
-                <aside className="mx_LeftPanel_roomListContainer">
+                <div className="mx_LeftPanel_roomListContainer">
                     { this.renderSearchDialExplore() }
                     { this.renderBreadcrumbs() }
                     { !this.props.isMinimized && (
@@ -401,7 +401,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                             { roomList }
                         </div>
                     </div>
-                </aside>
+                </div>
             </div>
         );
     }