Add detection and download of material_symbol icons in config/navigation.rb (#31366)

lib/tasks/icons.rake

@@ -38,6 +38,20 @@ def find_used_icons
     end
   end
 
+  Rails.root.join('config', 'navigation.rb').open('r') do |file|
+    pattern = /material_symbol\('(?<icon>[^']*)'\)/
+    file.each_line do |line|
+      match = pattern.match(line)
+      next if match.blank?
+
+      # navigation.rb only uses 400x24 icons, per material_symbol() in
+      # app/helpers/application_helper.rb
+      icons_by_weight_and_size[400] ||= {}
+      icons_by_weight_and_size[400][24] ||= Set.new
+      icons_by_weight_and_size[400][24] << match['icon']
+    end
+  end
+
   icons_by_weight_and_size
 end