Add AV1 OBU header parser and OBU types utilities

[JoeTurki]

Description

Implement AV1 bitstream format OBU header parser and utility functions for OBU types.

Reference issue

pion/webrtc#3036

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.18%. Comparing base (a78a4a6) to head (74a4302).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #294      +/-   ##
==========================================
+ Coverage   84.72%   85.18%   +0.46%     
==========================================
  Files          24       25       +1     
  Lines        2703     2788      +85     
==========================================
+ Hits         2290     2375      +85     
  Misses        354      354              
  Partials       59       59              

Flag	Coverage Δ
go	85.18% <100.00%> (+0.46%)	⬆️
wasm	84.57% <100.00%> (+0.48%)	⬆️

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[JoeTurki]

@Sean-Der Hello, This is a base for the packetizer and the depacketizer. After this is merged I'll do:

1. Continue the rest of my PR Implement av1 depacketizer #291 and make it construct a correct low bitstream, and construct OBU_temporal_delimiters.
2. Fix the packetizer, omit OBU_temporal_delimiters and construct correct RTP packets, I have a local version working, But I need to make correct tests.
3. Implement annex-b writer & reader, and fix the ivf writer and reader for AV1, and make OBU parsers (Need to parse the Sequence Headers at least).
4. Make more AV1 examples, and a Gstreamer test / example.

If things went well I'll be able to do all of this by or before the next weekend.

[Sean-Der]

Amazing work @JoeTurki, full steam ahead :)

The only thing I would do is add GStreamer/Chrome tests of AV1. I the effort vs value isn't worth it (IMO). I think it is ok to have a bunch of example video files and call it a day!

AV1 isn't going to change. However running GStreamer/Chrome is CI is frustrating. Especially if then a user has to run it locally to debug anything.