A fatal `PlaybackException` is mapped to a legacy playback state
in state `STATE_ERROR` with error code, message and extras. A
non-fatal error sent to controllers with `MediaSession.sendError`
is synced to the legacy session by setting error code and message
and merging the extras while preserving the rest of the state in
sync with the session player.
Vice versa, a `MediaController` connected to a legacy session receives
fatal errors through `Player.onPlayerErrorChanged()` and non-fatal errors
through `MediaController.Listener.onError()`.
Error codes are mapped in `LegacyConversions`. Values of error codes
in `@SessionError.ErrorCode` come from `@PlaybackExceptino.ErrorCode`
with the exception of `@SessionError.ERROR_IO` and
`@SessionError.ERROR_UNKNOWN`. These already exist in
`@PlaybackException.ErrorCode` and are mapped accordingly to avoid
semantic duplicates.
PiperOrigin-RevId: 642595517
011ed909c0