pass fromEl and toEl to hook beforeUpdate

Relates to #3615.

Allowing beforeUpdate to cancel an update by returning false is **not**
implemented, as this would require more complex internal changes.

Author: SteffenDE

assets/js/phoenix_live_view/view.js

@@ -438,7 +438,7 @@ export default class View {
     let hook = this.getHook(fromEl)
     let isIgnored = hook && DOM.isIgnored(fromEl, this.binding(PHX_UPDATE))
     if(hook && !fromEl.isEqualNode(toEl) && !(isIgnored && isEqualObj(fromEl.dataset, toEl.dataset))){
-      hook.__beforeUpdate()
+      hook.__beforeUpdate(fromEl, toEl)
       return hook
     }
   }

assets/js/phoenix_live_view/view_hook.js

@@ -32,7 +32,7 @@ export default class ViewHook {
 
   __mounted(){ this.mounted && this.mounted() }
   __updated(){ this.updated && this.updated() }
-  __beforeUpdate(){ this.beforeUpdate && this.beforeUpdate() }
+  __beforeUpdate(fromEl, toEl){ this.beforeUpdate && this.beforeUpdate(fromEl, toEl) }
   __destroyed(){
     this.destroyed && this.destroyed()
     DOM.deletePrivate(this.el, HOOK_ID) // https://github.com/phoenixframework/phoenix_live_view/issues/3496