just require the template resolver

LookupContext is eagerly loaded, and FallbackFileSystemResolver is
referenced at the class level.  Just require the resolver from the
eagerly loaded class rather than jumping through autoload hoops

actionview/lib/action_view.rb

@@ -56,7 +56,6 @@ module ActionView
     autoload_at "action_view/template/resolver" do
       autoload :Resolver
       autoload :PathResolver
-      autoload :FileSystemResolver
       autoload :OptimizedFileSystemResolver
       autoload :FallbackFileSystemResolver
     end

actionview/lib/action_view/lookup_context.rb

@@ -1,6 +1,7 @@
 require 'thread_safe'
 require 'active_support/core_ext/module/remove_method'
 require 'active_support/core_ext/module/attribute_accessors'
+require 'action_view/template/resolver'
 
 module ActionView
   # = Action View Lookup Context