Simplify adapter deprecation and delegation

The Adapter module was refactored a bit to use Active Support delegation
and remove duplicated code.
The CHANGELOG was also added.

CHANGELOG.md

@@ -29,6 +29,7 @@ Fixes:
 - [#1488](https://github.com/rails-api/active_model_serializers/pull/1488) Require ActiveSupport's string inflections (@nate00)
 
 Misc:
+- [#1559](https://github.com/rails-api/active_model_serializers/pull/1559) Add a deprecation DSL. (@bf4 @groyoh)
 - [#1543](https://github.com/rails-api/active_model_serializers/pull/1543) Add the changes missing from #1535. (@groyoh)
 - [#1535](https://github.com/rails-api/active_model_serializers/pull/1535) Move the adapter and adapter folder to
   active_model_serializers folder and changes the module namespace. (@domitian @bf4)

lib/active_model/serializer/adapter.rb

@@ -5,35 +5,18 @@ module ActiveModel
       class << self
         extend ActiveModelSerializers::Deprecate
 
-        def create(resource, options = {})
-          ActiveModelSerializers::Adapter.create(resource, options)
+        def self.delegate_and_deprecate(method)
+          delegate method, to: ActiveModelSerializers::Adapter
+          deprecate method, 'ActiveModelSerializers::Adapter.'
         end
-        deprecate :create, 'ActiveModelSerializers::Adapter.'
+        private_class_method :delegate_and_deprecate
 
-        def adapter_class(adapter)
-          ActiveModelSerializers::Adapter.adapter_class(adapter)
-        end
-        deprecate :adapter_class, 'ActiveModelSerializers::Adapter.'
-
-        def adapter_map
-          ActiveModelSerializers::Adapter.adapter_map
-        end
-        deprecate :adapter_map, 'ActiveModelSerializers::Adapter.'
-
-        def adapters
-          ActiveModelSerializers::Adapter.adapters
-        end
-        deprecate :adapters, 'ActiveModelSerializers::Adapter.'
-
-        def register(name, klass = name)
-          ActiveModelSerializers::Adapter.register(name, klass)
-        end
-        deprecate :register, 'ActiveModelSerializers::Adapter.'
-
-        def lookup(adapter)
-          ActiveModelSerializers::Adapter.lookup(adapter)
-        end
-        deprecate :lookup, 'ActiveModelSerializers::Adapter.'
+        delegate_and_deprecate :create
+        delegate_and_deprecate :adapter_class
+        delegate_and_deprecate :adapter_map
+        delegate_and_deprecate :adapters
+        delegate_and_deprecate :register
+        delegate_and_deprecate :lookup
       end
 
       require 'active_model/serializer/adapter/base'