Feature/dev 1165 edit element additional toolbar menu

[i-just]

Description

• element edit pages now contain an additional menu, which is placed after the save button; most buttons were moved to it;

• the additional menu also shows in a slideout, but in there, we don’t show any destructive options

• destructive items are at the end of the list

• base\Element class has a new getAdditionalMenuComponents() method, which should be used to add items to the additional menu;

• there’s also EVENT_DEFINE_ADDITIONAL_MENU_COMPONENTS event which can be used to add items to the menu;

  • the exception is the User element where EVENT_REGISTER_USER_ACTIONS is still used;
  • another deviation for the user edit form is that action components should reference data-form="userform" - see UsersController::actionEditUser() for more an example

• each component should be an array that can consist of:
  'label' => text to show in the a or button tag; can be an empty string
  'tag' => optional; defaults to a; you can use button too and hr if you want to add a visual separator between items
  'data' => optional; data attributes
  'aria' => optional; aria attributes
  'options' => optional; any other attributes, e.g. class

Related issues

dev-1165