_BridgedStoredNSError should conform to CustomStringConvertible

Since it is a struct that wraps an NSError, it should map its
`description` property to its internal NSError instance

Author: colemancda

stdlib/public/Darwin/Foundation/NSError.swift

@@ -417,7 +417,7 @@ extension _BridgedNSError where Self.RawValue: FixedWidthInteger {
 /// Describes a bridged error that stores the underlying NSError, so
 /// it can be queried.
 public protocol _BridgedStoredNSError :
-     _ObjectiveCBridgeableError, CustomNSError, Hashable {
+     _ObjectiveCBridgeableError, CustomNSError, Hashable, CustomStringConvertible {
   /// The type of an error code.
   associatedtype Code: _ErrorCodeProtocol, RawRepresentable
   where Code.RawValue: FixedWidthInteger
@@ -433,6 +433,12 @@ public protocol _BridgedStoredNSError :
   init(_nsError error: NSError)
 }
 
+public extension _BridgedStoredNSError {
+    var description: String {
+        return _nsError.description
+    }
+}
+
 /// Various helper implementations for _BridgedStoredNSError
 extension _BridgedStoredNSError {
   public var code: Code {