[3.x] New art assets for the Isometric Game demo

[Dynline]

Version 3.x

Changes

• Added new 8 directional character art and code for walk and idle animations
• added decoration sprites on the floor and walls
• updated tileset collisions and colors
• updated project icon
• added 2d lights, occlusions and additional sprites to fake more light/shadows on surfaces

This PR was sponsored by Ramatak with 💚

[Calinou]

Trailing whitespace should be removed in script and shader files as noted on the static checks CI. You can make the Godot editor do this automatically by enabling Text Editor > Behavior > Files > Trim Trailing Whitespace on Save in the Editor Settings, but note that you must save scripts/shaders again for this to take effect.

[Calinou]

Merged manually with https://github.com/godotengine/godot-demo-projects/commit/cdffdc025f1d9e117c8ac7a53e5bde51b6fb0743, with a few additional changes:

• Increased the goblin's animation speed to better match the movement speed and make it look smoother.
• Optimized images losslessly with OptiPNG.

Thanks again!