C# code for custom MainLoop missing critical attribute

[PastTheFuture]

Your Godot version: 4.2

Issue description:
C# code for MainLoop page missing critical attribute. As per this commit, in order for Godot to see your custom C# MainLoop, it needs to have the [GlobalClass] attribute. Without this attribute you get the message: "Error: MainLoop type doesn't exist: CustomMainLoop".

URL to the documentation page:
https://docs.godotengine.org/en/stable/classes/class_mainloop.html

Proposed code:

using Godot;

[GlobalClass]
public partial class CustomMainLoop : MainLoop
{
    private double _timeElapsed = 0;

    public override void _Initialize()
    {
        GD.Print("Initialized:");
        GD.Print($"  Starting Time: {_timeElapsed}");
    }

    public override bool _Process(double delta)
    {
        _timeElapsed += delta;
        // Return true to end the main loop.
        return Input.GetMouseButtonMask() != 0 || Input.IsKeyPressed(Key.Escape);
    }

    private void _Finalize()
    {
        GD.Print("Finalized:");
        GD.Print($"  End Time: {_timeElapsed}");
    }
}