iOS: add type to peer connection local streams

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 97 matching lines @@
 
 @end
 
 RTC_EXPORT
 @interface RTCPeerConnection : NSObject
 
 /** The object that will be notifed about events such as state changes and
  *  streams being added or removed.
  */
 @property(nonatomic, weak, nullable) id<RTCPeerConnectionDelegate> delegate;
-@property(nonatomic, readonly) NSArray *localStreams;
+@property(nonatomic, readonly) NSArray<RTCMediaStream *> *localStreams;
 @property(nonatomic, readonly, nullable)
     RTCSessionDescription *localDescription;
 @property(nonatomic, readonly, nullable)
     RTCSessionDescription *remoteDescription;
 @property(nonatomic, readonly) RTCSignalingState signalingState;
 @property(nonatomic, readonly) RTCIceConnectionState iceConnectionState;
 @property(nonatomic, readonly) RTCIceGatheringState iceGatheringState;
 
 /** Gets all RTCRtpSenders associated with this peer connection.
  *  Note: reading this property returns different instances of RTCRtpSender.
@@ skipping 86 matching lines @@
  */
 - (void)statsForTrack:
     (nullable RTCMediaStreamTrack *)mediaStreamTrack
      statsOutputLevel:(RTCStatsOutputLevel)statsOutputLevel
     completionHandler:
     (nullable void (^)(NSArray<RTCStatsReport *> *stats))completionHandler;
 
 @end
 
 NS_ASSUME_NONNULL_END