Warn when creating a script with the same name as the parent class

[aaronfranke]

This PR adds a warning when creating a script if the class name is the same as the parent class.

This is most useful for C# users, but it's also relevant for GDScript/VisualScript/GDNative users as well (for those, it's a best practice thing, not a technical limitation, or rather, a technical inconvenience).

For example, let's say that you created this Enemy class in C#, which is a KinematicBody3D:

public partial class Enemy : KinematicBody3D

Then you want to create a class for your player, but you forgot to rename the node to "Player" or similar, and you also forgot to change the name of the file to something other than KinematicBody3D.cs. So you get this:

public partial class KinematicBody3D : Godot.KinematicBody3D

The C# script generator has code to handle this case, so it will mark it as extending Godot.KinematicBody3D. However, this breaks the Enemy class, since now the behavior and variables from the player will show up inside Enemy, since Enemy is now extending KinematicBody3D from KinematicBody3D.cs instead of Godot.KinematicBody3D. To be clear, this is not a hypothetical problem, I've seen this happen to someone in the past.

• One solution would be to make all new scripts : Godot.Something instead of : Something, however there would still be confusion if someone used new KinematicBody3D instead of new Godot.KinematicBody3D.

• Also, even if this problem didn't exist (and it doesn't in GDScript etc), I would still recommend as a best practice that people don't name their scripts the same as a built-in type for the sake of clarity.

The solution I've come up with is this PR which will warn users if they try to create a script with the same name as the parent type. Really we would want to check if the class name is the same as any built-in type, but I'm not sure what's the best way to implement that, and checking if it's the same as the parent class will cover the most common cases for this warning.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.4.