Update controllers to use ContentItemLoader

- Now that ContentItemLoader handles caching we can use that rather than the stuff that the format constraints were putting into the request env.
- LandingPageController's scaffolding is still needed for the moment, but we can remove it soon (since part of this project is about replacing that scaffolding with a more generally useful one).

app/controllers/content_items_controller.rb

@@ -22,7 +22,7 @@ def publication_class
   end
 
   def content_item
-    @content_item ||= ContentItemFactory.build(request.env[:content_item] || request_content_item(content_item_slug || "/#{params[:slug]}"))
+    @content_item ||= ContentItemFactory.build(ContentItemLoader.load(content_item_slug || "/#{params[:slug]}"))
   end
 
   def content_item_slug
@@ -33,10 +33,6 @@ def content_item_hash
     @content_item_hash ||= content_item.to_h
   end
 
-  def request_content_item(base_path = "/#{params[:slug]}")
-    GdsApi.content_store.content_item(base_path)
-  end
-
   # NOTE: Frontend honours the max-age directive  provided
   # in Content Store's Cache-Control response header.
   def set_expiry(expiry = nil)

app/controllers/error_controller.rb

@@ -1,6 +1,8 @@
 class ErrorController < ApplicationController
   def handler
-    # defer any errors to be handled in ApplicationController
-    raise request.env[:content_item_error]
+    # We know at this point that the ContentItemLoader has stored
+    # an exception to deal with, so just retrieve it and raise it
+    # to be handled in ApplicationController
+    raise ContentItemLoader.load(request.path)
   end
 end

app/controllers/landing_page_controller.rb

@@ -5,8 +5,14 @@ class LandingPageController < ContentItemsController
 
   # SCAFFOLDING: can be removed when basic content items are available
   # from content-store
-  def request_content_item(_base_path)
-    GdsApi.content_store.content_item(request.path).to_h
+  def content_item
+    @content_item ||= ContentItemFactory.build(old_scaffolding_content_item)
+  end
+
+  # SCAFFOLDING: can be removed when basic content items are available
+  # from content-store
+  def old_scaffolding_content_item
+    ContentItemLoaderGdsApi.content_store.content_item(request.path).to_h
   rescue StandardError
     fake_data
   end