refactor: unify core actions and Ex command aliases

src/ruby_config.rb

@@ -124,7 +124,9 @@ module Vamp
     # @return [String]
     def external_command(command)
       name = Vamp.string!(command, "binding command")
-      raise TypeError, "use config.core for built-in actions" if name.start_with?("core.")
+      if name.start_with?("core.") || Vamp.builtin_command?(name)
+        raise TypeError, "use config.core for built-in actions"
+      end
 
       name
     end