[Foundation] URL: Add hash(into:) implementation

Note: URL does not implement Hashable.

Author: lorentey

Darwin/Foundation-swiftoverlay/URL.swift

@@ -622,10 +622,14 @@ public struct URL : ReferenceConvertible, Equatable {
         _url = URL._converted(from: NSURL(fileURLWithFileSystemRepresentation: path, isDirectory: isDirectory, relativeTo: baseURL))
     }
 
-    public var hashValue: Int {
+    public var hashValue: Int { // FIXME(hashValue): This should be removed once URL implements Hashable.
         return _url.hash
     }
-    
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(_url)
+    }
+
     // MARK: -
 
     /// Returns the data representation of the URL's relativeString.