Navigation: Refactor mobile menu into it's own component (#41308)

* Navigation: Start creating new NavBarMenu component

* Navigation: Apply new NavBarMenu to NavBarNext

* Navigation: Remove everything to do with .sidemenu-open--xs

* Navigation: Ensure search is passed to NavBarMenu

* Navigation: Standardise NavBarMenuItem

* This extra check isn't needed anymore

* Navigation: Refactor <li> out of NavBarMenu

* Navigation: Combine NavBarMenuItem with DropdownChild

* use spread syntax since performance shouldn't be a concern for such small arrays

* Improve active item logic

* Ensure unique keys

* Remove this duplicate code

* Add unit tests for getActiveItem

* Add tests for NavBarMenu

* Rename mobileMenuOpen -> menuOpen in NavBarNext (since it can be used for mobile menu or megamenu)

* just use index to key the items

* Use exact versions of @react-aria packages

* Navigation: Make the dropdown header a NavBarMenuItem

* Navigation: Stop using dropdown-menu for styles

* Navigation: Hide divider in NavBarMenu + tweak color on section header

public/app/routes/GrafanaCtrl.ts

@@ -118,10 +118,6 @@ export function grafanaAppDirective() {
 
       $('.preloader').remove();
 
-      appEvents.on(CoreEvents.toggleSidemenuMobile, () => {
-        body.toggleClass('sidemenu-open--xs');
-      });
-
       appEvents.on(CoreEvents.toggleSidemenuHidden, () => {
         body.toggleClass('sidemenu-hidden');
       });