[Layout] Rename ASLayoutable to ASLayoutElement (#2290)

* [Layout API] Rename ASLayoutable to ASLayoutElement

* arg

* fix wrapperWithLayoutElement

* [Layout API] Rename ASLayoutable to ASLayoutElement

* arg

* address Michael's comments

* Remove ASLayoutValidation files that were deleted on master since this diff was created.

AsyncDisplayKit/Layout/ASLayoutElementExtensibility.h

@@ -0,0 +1,29 @@
+//
+//  ASLayoutElementExtensibility.h
+//  AsyncDisplayKit
+//
+//  Created by Michael Schneider on 3/29/16.
+//
+//  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+//
+
+#import <UIKit/UIGeometry.h>
+
+@protocol ASLayoutElementExtensibility <NSObject>
+
+// The maximum number of extended values per type are defined in ASEnvironment.h above the ASEnvironmentStateExtensions
+// struct definition. If you try to set a value at an index after the maximum it will throw an assertion.
+
+- (void)setLayoutOptionExtensionBool:(BOOL)value atIndex:(int)idx;
+- (BOOL)layoutOptionExtensionBoolAtIndex:(int)idx;
+
+- (void)setLayoutOptionExtensionInteger:(NSInteger)value atIndex:(int)idx;
+- (NSInteger)layoutOptionExtensionIntegerAtIndex:(int)idx;
+
+- (void)setLayoutOptionExtensionEdgeInsets:(UIEdgeInsets)value atIndex:(int)idx;
+- (UIEdgeInsets)layoutOptionExtensionEdgeInsetsAtIndex:(int)idx;
+
+@end