Merge pull request #15917 from luke-gru/actionview_perf

remove Set.new from DetailsKey::get, impacts rendering overhead

actionview/lib/action_view/lookup_context.rb

@@ -66,7 +66,7 @@ class DetailsKey #:nodoc:
       def self.get(details)
         if details[:formats]
           details = details.dup
-          syms    = Set.new Mime::SET.symbols
+          syms    = Mime::SET.symbols
           details[:formats] = details[:formats].select { |v|
             syms.include? v
           }