Build dynamic iOS SDK.

- Places most ObjC code into webrtc/sdk/objc instead.
- New gyp targets to build, strip and export symbols for dylib.
- Removes old script used to generate dylib.

BUG=

Review URL: https://codereview.webrtc.org/1903663002

Cr-Commit-Position: refs/heads/master@{#12524}

webrtc/sdk/objc/Framework/Classes/RTCAudioTrack+Private.h

@@ -0,0 +1,30 @@
+/*
+ *  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.
+ */
+
+#import "WebRTC/RTCAudioTrack.h"
+
+#include "webrtc/api/mediastreaminterface.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class RTCPeerConnectionFactory;
+@interface RTCAudioTrack ()
+
+/** AudioTrackInterface created or passed in at construction. */
+@property(nonatomic, readonly)
+    rtc::scoped_refptr<webrtc::AudioTrackInterface> nativeAudioTrack;
+
+/** Initialize an RTCAudioTrack with an id. */
+- (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
+                        trackId:(NSString *)trackId;
+
+@end
+
+NS_ASSUME_NONNULL_END