Add channel information to peer_packet signal in SceneMultiplayer

[SasaSuppenknecht]

This PR adds the channel information of a received packet to the peer_packet signal in SceneMultiplayer.

Previously, the signature was:
peer_packet(int id, PackedByteArray data)

And now it is:
peer_packet(int id, PackedByteArray data, int channel)

This PR is based on godotengine/godot-proposals#12907. The proposal suggests including a new signal for backwards compatibility, however, this kind of redundancy does not seem like a good fit for the engine. I also selected the channel information to be the last argument, as to be symmetrical to SceneMultiplayer.send_bytes.

[AThousandShips]

The proposal suggests including a new signal for backwards compatibility, however, this kind of redundancy does not seem like a good fit for the engine.

The suggestion of a new signal would be the better option as this breaks compatibility in a pretty significant way, as there's no way to automatically adjust to changes to signals, and no editor warning or indication of the change

[SasaSuppenknecht]

The suggestion of a new signal would be the better option as this breaks compatibility in a pretty significant way, as there's no way to automatically adjust to changes to signals, and no editor warning or indication of the change

Ah, makes sense. Then I will do as suggested in the initial proposal and add a new signal peer_packet_with_channel that contains the channel in its signature.