Temporary commit to help reviewer:

- The changes are quite substantial and creates a lot of diff hunks.
  This is going to be difficult to review so I opted to create
  *new file with existing class/module name* so that tests doesn't
  need to be modified and reviewers can focus on the implementation.

  This commit renames the previous Logger and TaggedLogging module.

activesupport/lib/active_support/logger.rb

@@ -5,7 +5,7 @@
 require "logger"
 
 module ActiveSupport
-  class Logger < ::Logger
+  class OldLogger < ::Logger
     include LoggerSilence
 
     # Returns true if the logger destination matches one of the sources

activesupport/lib/active_support/tagged_logging.rb

@@ -27,7 +27,7 @@ module ActiveSupport
   # This is used by the default Rails.logger as configured by Railties to make
   # it easy to stamp log lines with subdomains, request ids, and anything else
   # to aid debugging of multi-user production applications.
-  module TaggedLogging
+  module OldTaggedLogging
     module Formatter # :nodoc:
       # This method is invoked when a log event occurs.
       def call(severity, timestamp, progname, msg)