Simplify using helper methods in components

The `use_helpers` method was added in ViewComponent 3.8.0, and it's
included by default in all components since version 3.11.0.

Note we sometimes delegated the `can?` method to the controller instead
of the helpers, for no particularly reason. We're unifying that code as
well.

app/components/layout/admin_header_component.rb

@@ -1,6 +1,6 @@
 class Layout::AdminHeaderComponent < ApplicationComponent
   attr_reader :user
-  delegate :namespace, :namespaced_root_path, :show_admin_menu?, to: :helpers
+  use_helpers :namespace, :namespaced_root_path, :show_admin_menu?
 
   def initialize(user)
     @user = user