C#: New RPCAttribute

[raulsntos]

Replace old RPC attributes with a new single RPCAttribute which works like the GDScript @rpc annotation.

Follow-up to #49882

Usage

I copied the examples from the original core PR and adapted them to C# for comparison.

Example 1

# defaults are authority, no call_local, reliable, "default channel" (i.e. 0).
@rpc
func ping():
	print("Ping from: ", multiplayer.get_remote_sender_id())

// defaults are authority, no call_local, reliable, "default channel" (i.e. 0).
[RPC]
public void Ping()
{
	GD.Print($"Ping from: {Multiplayer.GetRemoteSenderId()}");
}

Example 2

# makes the RPC callable by anyone, "call_local", use "unreliable" transfer, channel 1
@rpc(any_peer, call_local, unreliable, 1)
func ping():
	print("Ping from: ", multiplayer.get_remote_sender_id())

// makes the RPC callable by anyone, "call_local", use "unreliable" transfer, channel 1
[RPC(RPCMode.AnyPeer, CallLocal = true, TransferMode = TransferMode.Unreliable, TransferChannel = 1)]
public void Ping()
{
	GD.Print($"Ping from: {Multiplayer.GetRemoteSenderId()}");
}

Alternative Designs

CallLocal

The CallLocal property is currently implemented as a boolean just like it is defined in the RPCConfig struct but it could be implemented as an enum with members Local and Remote to more closely resemble the GDScript syntax which uses call_local/call_remote.

public enum CallMode { Local, Remote }

Example

@rpc(..., call_local, ...)
@rpc(..., call_remote, ...)

[RPC(..., CallLocal = true, ...)] // Current
[RPC(..., CallMode = CallMode.Local, ...)] // Alternative

[RPC(..., CallLocal = false, ...)] // Current
[RPC(..., CallMode = CallMode.Remote, ...)] // Alternative

[neikeq]

This one is fine as well, but I prefer any future PRs be hold until the dotnet6 branch is merged.

[akien-mga]

Thanks!