Convert and cache GTA 3 assets in data directory

[atirut-w]

This feature serves a few purposes

• Instead of interpreting the game assets every time they are loaded, they can be interpreted once, saved as engine-native resource files, and loaded hopefully more quickly.
• Simpler asset streaming system.
• Hopefully, threaded asset loading using Godot's inbuilt solution

[Koalamana9]

This would be the way to go!