push extract_scale to the Type.

  - `extract_precision`, `extract_limit`, and `extract_default` probably need to follow.
  - would be good to remove the delegation `Column#extract_scale`.

/cc @sgrif

activerecord/lib/active_record/connection_adapters/column.rb

@@ -69,7 +69,7 @@ def extract_default(default)
       end
 
       private
-        delegate :extract_scale, to: Type
+        delegate :extract_scale, to: :cast_type
 
         def extract_limit(sql_type)
           $1.to_i if sql_type =~ /\((.*)\)/

activerecord/lib/active_record/connection_adapters/postgresql/column.rb

@@ -123,12 +123,6 @@ def extract_limit(sql_type)
           end
         end
 
-        # Extracts the scale from PostgreSQL-specific data types.
-        def extract_scale(sql_type)
-          # Money type has a fixed scale of 2.
-          sql_type =~ /^money/ ? 2 : super
-        end
-
         # Extracts the precision from PostgreSQL-specific data types.
         def extract_precision(sql_type)
           if sql_type == 'money'

activerecord/lib/active_record/connection_adapters/postgresql/oid.rb

@@ -39,6 +39,10 @@ def cast_value(value)
         class Money < Type::Decimal
           include Infinity
 
+          def extract_scale(sql_type)
+            2
+          end
+
           def cast_value(value)
             return value unless ::String === value
 

activerecord/lib/active_record/connection_adapters/type/value.rb

@@ -4,6 +4,10 @@ module Type
       class Value # :nodoc:
         def type; end
 
+        def extract_scale(sql_type)
+          Type.extract_scale(sql_type)
+        end
+
         def type_cast(value)
           cast_value(value) unless value.nil?
         end