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/views/elements/ServerPicker.tsx

@@ -85,8 +85,13 @@ const ServerPicker = ({ title, dialogTitle, serverConfig, onServerConfigChange }
     }
 
     return <div className="mx_ServerPicker">
-        <h3>{ title || _t("Homeserver") }</h3>
-        { !disableCustomUrls ? <AccessibleButton className="mx_ServerPicker_help" onClick={onHelpClick} /> : null }
+        <h2>{ title || _t("Homeserver") }</h2>
+        { !disableCustomUrls ? (
+            <AccessibleButton
+                className="mx_ServerPicker_help"
+                onClick={onHelpClick}
+                aria-label={_t("Help")}
+            />): null }
         <span className="mx_ServerPicker_server" title={typeof serverName === "string" ? serverName : undefined}>
             { serverName }
         </span>