SDF Global Illumination Implementation

[Snowapril]

According to Godot documentation and the developer's twit, VoxelGI is not proper to dynamically generated geometry mesh in runtime (https://docs.godotengine.org/en/latest/classes/class_voxelgi.html, https://twitter.com/reduzio/status/1401589094237540364)

As VoxFlow will generate fluid via CubbyFlow in real time, SDFGI seems more desirable for this project.

[Snowapril]

reference : Signed Distance Fields Dynamic Diffuse Global Illumination arXiv:2007.14394 [cs.GR]

[Snowapril]

reference : Two-Level Radiance Caching for Fast and Scalable Real-Time Global Illumination in Games
(https://gpuopen.com/gdc-presentations/2023/GDC-2023-Two-Level-Radiance-Caching-GI.pdf)

[Snowapril]

SDF GI implementation for VoxFlow rendering system will adopt godot's sdfgi.

[Snowapril]

https://jose-villegas.github.io/post/deferred_voxel_shading/