Update custom drawing in 2d to Godot4

This tutorial had 2 main issues: the code wasn't adapted to Godot
4 syntax and API and the suggested tutorial contained information
to workaround the (at the time) non existence of the `draw_arc()`
function.

A general update has been made, keeping the general structure but
changing the example for something more useful and fun
(replicating the godot logo with draw primitives) and an
additional example with a dynamicaly built drawing (dynamic line).

Too many informalities have been removed on the initial paragraph.
Fixed references to Texture instead of Texture2D.
Fixed old style of exporting properties to the editor.
Fixed inconsistencies calling Node2D, myNode2D and customNode2D.
Moved examples to the end of the page, leaving general information
at the top, and completing that info with images and references.
Removed references to an old demo project (Tetris).

Fixes godotengine#4184
Fixes godotengine#7521

Co-authored-by: Raul Santos <[email protected]>
Co-authored-by: A Thousand Ships <[email protected]>

Author: 3 people