FXAA for Godot 4 Compatibility Renderer

A Godot 4 project containing:

• Two FXAA shaders. One canvas_item, and one spatial
• Two example scenes using the effect
• Bonus edge detection shader included with the canvas_item example

Based on this project for Godot 3: https://github.com/atomius0/Godot-3.1-FXAA-Shader

This is an implementation of FXAA for Compatibility Renderer in Godot 4, a feature that has been absent since the release of Godot 4.

FXAA (Fast Approximate Anti-Aliasing) is a cheap alternative to super-sampling AA (Scaling 3D).