* Set the action label properly.
* Set the kebab icon as a decorative icon.
* Move the title attribute to the menu button itself instead of the
kebab icon.
- Update and improve styles for .btn-icon helper class for consistency.
- Added new $btn-icon-border-radius SCSS variable to cuztomize the btn-icon
border radius.
- Fix and simplify current .btn-icon usages
* Use the namespaced classes in imports instead of their aliases
* Add missing imports
* Add moved `\core\output\local\action_menu\subpanel` in the upgrade
notes
Jun Pataleta