MM-54191 Change how menu item click handlers are triggered after menus fully close (#24335)

* MM-54191 Change how menu item click handlers are triggered after menus fully close

* Switch menu items to use onClick instead of onMouseDown

* Add unit tests for menu keyboard navigation and opening modals

* Fix missing use of useMenuContextValue

* Remove unneeded ?.

* Fix unrelated test broken by @testing-library/user-event update

webapp/channels/package.json

@@ -106,7 +106,7 @@
     "@redux-devtools/extension": "3.2.3",
     "@testing-library/jest-dom": "5.16.4",
     "@testing-library/react": "12.1.4",
-    "@testing-library/user-event": "12.1.4",
+    "@testing-library/user-event": "13.5.0",
     "@types/bootstrap": "4.5.0",
     "@types/country-list": "2.1.0",
     "@types/enzyme": "3.10.11",