Add AV1 encoder&decoder wrappers for iOS SDK.

It is now possible to use AV1 encoder and decoder on iOS and test
them in apps like AppRTCMobile.

Bug: None
Change-Id: Ifae221020e5abf3809010676862eecd9ffeec5e3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208400
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33378}

sdk/objc/api/video_codec/RTCVideoDecoderAV1.h

@@ -0,0 +1,27 @@
+/*
+ *  Copyright 2021 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 <Foundation/Foundation.h>
+
+#import "RTCMacros.h"
+#import "RTCVideoDecoder.h"
+
+RTC_OBJC_EXPORT
+@interface RTC_OBJC_TYPE (RTCVideoDecoderAV1) : NSObject
+
+/* This returns a AV1 decoder that can be returned from a RTCVideoDecoderFactory injected into
+ * RTCPeerConnectionFactory. Even though it implements the RTCVideoDecoder protocol, it can not be
+ * used independently from the RTCPeerConnectionFactory.
+ */
++ (id<RTC_OBJC_TYPE(RTCVideoDecoder)>)av1Decoder;
+
++ (bool)isSupported;
+
+@end