Move internal dependencies into the main Engine body

This loads dependencies from `lib/hyrax` and dry-rb explictly from
Hyrax::Engine, instead of waiting until the initializer.

This is an alternate implementation to the one in
#3472

lib/hyrax/engine.rb

@@ -2,9 +2,11 @@ module Hyrax
   class Engine < ::Rails::Engine
     isolate_namespace Hyrax
 
-    # These gems must be required outside of an initializer or they don't get loaded.
     require 'awesome_nested_set'
     require 'breadcrumbs_on_rails'
+    require 'dry/struct'
+    require 'dry/equalizer'
+    require 'dry/validation'
     require 'jquery-ui-rails'
     require 'flot-rails'
     require 'almond-rails'
@@ -15,6 +17,11 @@ class Engine < ::Rails::Engine
     require 'legato'
     require 'pul_uv_rails'
 
+    require 'hydra/derivatives'
+    require 'hyrax/controller_resource'
+    require 'hyrax/search_state'
+    require 'hyrax/errors'
+
     # Force these models to be added to Legato's registry in development mode
     config.eager_load_paths += %W[
       #{config.root}/app/models/hyrax/download.rb
@@ -62,14 +69,7 @@ class Engine < ::Rails::Engine
     end
 
     initializer 'requires' do
-      require 'hydra/derivatives'
-      require 'hyrax/controller_resource'
-      require 'hyrax/search_state'
-      require 'hyrax/errors'
       require 'power_converters'
-      require 'dry/struct'
-      require 'dry/equalizer'
-      require 'dry/validation'
     end
 
     initializer 'routing' do