views: factor out FontAwesome icons.

Factor out FontAwesome icons into a set of helpers. This is so that it's
easier to keep track of which icons we're using and easier to change
icons globally.

app/components/popup_menu_component.rb

@@ -2,6 +2,7 @@
 
 class PopupMenuComponent < ApplicationComponent
   include ViewComponent::SlotableV2
+  delegate :ellipsis_icon, to: :helpers
 
   renders_many :items
 end