Add Godot.SignalAwaiter class documentation and reference

[Mek101]

Your Godot version: 3.2.1 Issue description: There's no documentation regarding the public class SignalAwaiter. It should also be noted that it's the object type returned by Node.ToSignal, and awaiting it consumes the object, therefore requiring to create a new SignalAwaiter every time. URL to the documentation page (if already existing): It should be cited also here(?) https://docs.godotengine.org/en/stable/getting_started/scripting/c_sharp/c_sharp_differences.html#yield

[Calinou]

cc @neikeq

[Mek101]

cc @neikeq

Sorry?

[Calinou]

@Mek101 I was carbon-copying neikeq so he could see this thread more easily :slightly_smiling_face:

He's the primary C# maintainer for Godot.

[Perustaja]

Any update on this?