We didn't used to do that because it would have required us to serialize and
then de-serialize as MCProtocolLib only to re-serialize each packet.
With ReplayStudio v2, we only have to convert to from MC's ByteBuf types to
ReplayStudio's ByteBuf (fairly trivial).
This also allows us to automatically make use of ReplayStudio's backwards
compatibility features: We didn't used to record the login phase pre-1.14 and we
still don't, so we now would have to inject a fake login packet (because we're
no longer generating legacy-version replay files) but ReplayOutputStream can
do that for us.
Without this commit, any pre-1.14 replays generated are unplayable due to the
missing LoginSuccess packet.
05f617a885