Lazy load the type_map

In hopes of allowing the configuration for emulate_booleans to get set
before it is evaluated.

Author: andynu

lib/active_record/connection_adapters/oracle_enhanced_adapter.rb

@@ -691,6 +691,12 @@ def check_version
       end
 
       class << self
+
+          def type_map
+            @type_map ||= Type::TypeMap.new.tap { |m| initialize_type_map(m) }
+            @type_map
+          end
+
         private
           def initialize_type_map(m)
             super
@@ -724,10 +730,9 @@ def initialize_type_map(m)
           end
       end
 
-      TYPE_MAP = Type::TypeMap.new.tap { |m| initialize_type_map(m) }
 
       def type_map
-        TYPE_MAP
+        self.class.type_map
       end
 
       def extract_value_from_default(default)