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

test/components/views/messages/__snapshots__/DateSeparator-test.tsx.snap

@@ -6,7 +6,7 @@ exports[`DateSeparator renders the date separator correctly 1`] = `
   roomId="!unused:example.org"
   ts={1639728540000}
 >
-  <h2
+  <div
     aria-label="Today"
     className="mx_DateSeparator"
     role="separator"
@@ -15,15 +15,15 @@ exports[`DateSeparator renders the date separator correctly 1`] = `
     <hr
       role="none"
     />
-    <div
+    <h2
       aria-hidden="true"
     >
       Today
-    </div>
+    </h2>
     <hr
       role="none"
     />
-  </h2>
+  </div>
 </DateSeparator>
 `;
 
@@ -33,7 +33,7 @@ exports[`DateSeparator when feature_jump_to_date is enabled renders the date sep
   roomId="!unused:example.org"
   ts={1639728540000}
 >
-  <h2
+  <div
     aria-label="Fri, Dec 17 2021"
     className="mx_DateSeparator"
     role="separator"
@@ -88,11 +88,11 @@ exports[`DateSeparator when feature_jump_to_date is enabled renders the date sep
             role="button"
             tabIndex={0}
           >
-            <div
+            <h2
               aria-hidden="true"
             >
               Fri, Dec 17 2021
-            </div>
+            </h2>
             <div
               className="mx_DateSeparator_chevron"
             />
@@ -103,6 +103,6 @@ exports[`DateSeparator when feature_jump_to_date is enabled renders the date sep
     <hr
       role="none"
     />
-  </h2>
+  </div>
 </DateSeparator>
 `;

test/components/views/settings/__snapshots__/FontScalingPanel-test.tsx.snap

@@ -31,6 +31,7 @@ exports[`FontScalingPanel renders the font scaling UI 1`] = `
             <div
               aria-label="Loading..."
               className="mx_Spinner_icon"
+              role="progressbar"
               style={
                 Object {
                   "height": 32,