Outdated docs: Custom Drawing in 2D

[halotroop2288]

Your Godot version:
4.0 -> latest

Issue description:
Outdated documentation, as evidenced by incorrect (Godot 3-style) export example code.
This may or may not be the only mistake on the page. As someone who has not performed this before without the documentation, I can't comment on that.

This page also needs attention since October 2020, see #4184.

URL to the documentation page:
https://docs.godotengine.org/en/stable/tutorials/2d/custom_drawing_in_2d.html#updating

[jynus]

Thank you for the report.

I think I was one of the latest persons to update that page, but only to replace the outdated call to rad2deg() at 6865811 and there I tested that code block, but didn't do a full review of the page and missed those old code blocks.

Let me do it now and test all code excerpts so we can remove the warning (the warning says it is updated, not outdated), but I may need review from someone that may be a Godot 4 beginner (meaning less blind to documentation mistakes). :-) It may take a bit because that's a relatively long page and I will have to test it on both GDScript and C#

[jynus]

As mentioned before, kindly asking for feedback on the refactor sent at #7532, specially from those not already familiar with the _draw() methods from CanvasItem to see if the proposed new redaction is more useful.