mrp: Major updates to protobuf messages

[postlund]

Added more protobuf types, some new message definitions introduced in
tvOS 14 and moved playback state to common.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@3eb9d3a). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #912   +/-   ##
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  Coverage          ?   95.64%           
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  Files             ?       38           
  Lines             ?     3258           
  Branches          ?        0           
=========================================
  Hits              ?     3116           
  Misses            ?      142           
  Partials          ?        0           

Flag	Coverage Δ
unittests	95.64% <0.00%> (?)

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