Split iOS sdk in to separate targets

This CL splits the iOS sdk into separate static libraries for video,
audio, ui, common, and peerconnection-related code. This will in the
future make it easier to compile WebRTC without unneeded components.

BUG=webrtc:4867

Review-Url: https://codereview.webrtc.org/2862543002
Cr-Commit-Position: refs/heads/master@{#18166}

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

@@ -1,42 +0,0 @@
-/*
- *  Copyright 2016 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/RTCMediaSource.h"
-
-#include "webrtc/api/mediastreaminterface.h"
-
-NS_ASSUME_NONNULL_BEGIN
-
-typedef NS_ENUM(NSInteger, RTCMediaSourceType) {
-  RTCMediaSourceTypeAudio,
-  RTCMediaSourceTypeVideo,
-};
-
-@interface RTCMediaSource ()
-
-@property(nonatomic, readonly)
-    rtc::scoped_refptr<webrtc::MediaSourceInterface> nativeMediaSource;
-
-- (instancetype)initWithNativeMediaSource:
-   (rtc::scoped_refptr<webrtc::MediaSourceInterface>)nativeMediaSource
-                                     type:(RTCMediaSourceType)type
-    NS_DESIGNATED_INITIALIZER;
-
-+ (webrtc::MediaSourceInterface::SourceState)nativeSourceStateForState:
-    (RTCSourceState)state;
-
-+ (RTCSourceState)sourceStateForNativeState:
-    (webrtc::MediaSourceInterface::SourceState)nativeState;
-
-+ (NSString *)stringForState:(RTCSourceState)state;
-
-@end
-
-NS_ASSUME_NONNULL_END