Fix #1759, Grape integration, adds serialization_context

- improves improves serialization_context to take options and not depend
on a `request` object.
- adds descriptive error on missing serialization_context.
- Document overriding `CollectionSerializer#paginated?`.

lib/grape/helpers/active_model_serializers.rb

@@ -1,4 +1,7 @@
 # Helpers can be included in your Grape endpoint as: helpers Grape::Helpers::ActiveModelSerializers
+
+require 'active_model_serializers/serialization_context'
+
 module Grape
   module Helpers
     module ActiveModelSerializers
@@ -8,6 +11,12 @@ module Grape
       #
       # Example: To include pagination meta data: render(posts, meta: { page: posts.page, total_pages: posts.total_pages })
       def render(resource, active_model_serializer_options = {})
+        active_model_serializer_options.fetch(:serialization_context) do
+          active_model_serializer_options[:serialization_context] = ::ActiveModelSerializers::SerializationContext.new(
+            original_url: request.url[/\A[^?]+/],
+            query_parameters: request.params
+          )
+        end
         env[:active_model_serializer_options] = active_model_serializer_options
         resource
       end