fix(node): Cache the full VoiceStateUpdate; fixes `Player.moveTo()`

[Zoddo]

Currently, only the session_id is cached. When needed, a VoiceStateUpdate is reconstructed by the getter Player.voiceState. However, this "reconstructed" VSU is missing the channel_id property. This break Player.moveTo(), because it calls Node.voiceStateUpdate() with this partial VSU, which is basically a noop without a channel_id.

This commit fixes this issue by caching the full VoiceStateUpdate (which includes the channel_id) in the Node.voiceStates Map.

This is the cleanest way I found.

• I cannot cache the channel_id in the Player, because it may not exists yet when Node.voiceStateUpdate() is called (and creating it at this point may be undesirable).
• Creating another Map just to cache the channel_id looks wrong.
• Passing a fake channel_id to Node.voiceStateUpdate() would works, but it's a ugly fix.

For the record, Player.moveTo() appears to have been broken by the commit 551792856fa110c499d87bc4a34e49d5835e2f09 which changed the behavior of Node.voiceStateUpdate() when the channel_id property is missing.

[appellation]

Ah, excellent catch and thanks for explaining. I think this is probably the most reasonable solution. Initially we were only storing the session ID in an attempt to reduce memory usage; however, especially since it's lossy, I think that was a bit of premature optimization.

551792856fa110c499d87bc4a34e49d5835e2f09 is also an attempt to avoid memory leaks and I believe the logic there is sound; if the VSU packet has a null channel ID, the connection is being terminated.

[Zoddo]

If we want to reduce a bit the memory usage, we can do something like:

this.voiceStates.set(packet.guild_id, {
  guild_id: packet.guild_id,
  channel_id: packet.channel_id,
  user_id: packet.user_id,
  session_id: packet.session_id,
});

This would notably remove the member object from the VSU, which is likely half of its size

[appellation]

Is there a need for the member object? If not, I suggest we move forward with cutting it out.