[NoCopyRendering] Use vm instead of malloc (#833)

* [Contexts] Use mmap directly for possible perf gain and to tag the memory as CGImage

* Wrap the mmap in an object

* Go straight to dataprovider

* Tweak it

* Remove wrong comment

* Finish that comment

* Address warnings

Source/ASCGImageBuffer.h

@@ -0,0 +1,31 @@
+//
+//  ASCGImageBuffer.h
+//  Texture
+//
+//  Copyright (c) 2018-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import <Foundation/Foundation.h>
+#import <AsyncDisplayKit/ASBaseDefines.h>
+#import <CoreGraphics/CGDataProvider.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+AS_SUBCLASSING_RESTRICTED
+@interface ASCGImageBuffer : NSObject
+
+- (instancetype)initWithLength:(NSUInteger)length;
+
+@property (readonly) void *mutableBytes NS_RETURNS_INNER_POINTER;
+
+/// Don't do any drawing or call any methods after calling this.
+- (CGDataProviderRef)createDataProviderAndInvalidate;
+
+@end
+
+NS_ASSUME_NONNULL_END