DockedMegaMenu: Keep undock button (#78461)

* dock undock smoothly

* handle keyboard focus

* use ref instead of state

* run i18n:extract

* undo this change

* make dock/undock first button to focus

* only focus when going to docked, add comment

* minor tweaks

public/locales/fr-FR/grafana.json

@@ -941,7 +941,8 @@
     },
     "megamenu": {
       "close": "Fermer le menu",
-      "dock": "Ancrer le menu"
+      "dock": "Ancrer le menu",
+      "undock": ""
     },
     "toolbar": {
       "close-menu": "Fermer le menu",