Foundation: change Data.Indices to be a CountableRange<Int>, that is much faster than the default

Author: gribozavr

stdlib/public/SDK/Foundation/Data.swift

@@ -81,7 +81,7 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
     public typealias Base64DecodingOptions = NSData.Base64DecodingOptions
 
     public typealias Index = Int
-    public typealias Indices = DefaultRandomAccessIndices<Data>
+    public typealias Indices = CountableRange<Int>
 
     internal var _wrapped : _SwiftNSData
 
@@ -642,6 +642,10 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
         return i + 1
     }
 
+    public var indices: CountableRange<Int> {
+        return startIndex..<endIndex
+    }
+
     /// An iterator over the contents of the data.
     ///
     /// The iterator will increment byte-by-byte.