Add custom logger for runtime error printing

[MrMinimal]

I merged the code of your amazing logger demo into this project because showing errors is useful.

Things to improve

• I have no clue how to properly do UI in Godot, the error panel size is not dynamic
• The error output is a bit cryptic as the file name of the ingame script is a negative integer

I don't have much time to contribute more atm, but I am thankful for this project. Reading documentation on loggers didn't get me far but looking at the demo is when it clicked for me. It should be part of the official demos imho.

References

Logger feature https://github.com/godotengine/godot/pull/91006 Your amazing logger demo https://github.com/godotengine/godot-demo-projects/pull/1242.

Feel free to edit to your liking, it's just a proof of concept