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/subnavigation_component.rb

@@ -1,3 +1,3 @@
 class Layout::SubnavigationComponent < ApplicationComponent
-  delegate :content_block, :layout_menu_link_to, to: :helpers
+  use_helpers :content_block, :layout_menu_link_to
 end