Expose AV1 encoder&decoder from Android SDK.

Bug: None
Change-Id: Ie32be36da498d4bed2a3cf51aa6abc8838e42da1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212024
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Commit-Queue: Yura Yaroshevich <yura.yaroshevich@gmail.com>
Cr-Commit-Position: refs/heads/master@{#33743}

sdk/android/api/org/webrtc/VideoEncoder.java

@@ -86,6 +86,8 @@ public interface VideoEncoder {
 
   public class CodecSpecificInfoH264 extends CodecSpecificInfo {}
 
+  public class CodecSpecificInfoAV1 extends CodecSpecificInfo {}
+
   /**
    * Represents bitrate allocated for an encoder to produce frames. Bitrate can be divided between
    * spatial and temporal layers.