Add initial Sponza benchmark

[franciscod]

I've imported the scene from https://github.com/Calinou/godot-sponza/tree/4.0-dev

There are three basic benchmarks:

• ambient only
• directional light + shadows
• omni lights + shadows

Sample results:

$ godot -- --run-benchmarks --include-benchmarks="rendering/sponza/*" | grep '{"benchmarks' | tee results.json | jq ".benchmarks | map(select(.results != {}))"
[
  {
    "category": "Rendering > Sponza",
    "name": "Sponza Ambient",
    "results": {
      "idle": 0,
      "physics": 0,
      "render_cpu": 0.192,
      "render_gpu": 2.474,
      "time": 0.12
    }
  },
  {
    "category": "Rendering > Sponza",
    "name": "Sponza Directional",
    "results": {
      "idle": 0,
      "physics": 0,
      "render_cpu": 0.09689,
      "render_gpu": 3.594,
      "time": 0.066
    }
  },
  {
    "category": "Rendering > Sponza",
    "name": "Sponza Omni",
    "results": {
      "idle": 0,
      "physics": 0,
      "render_cpu": 0.07761,
      "render_gpu": 7.137,
      "time": 0.06
    }
  }
]

[Calinou]

I've pushed commits that convert Sponza to glTF + lossless WebP for smaller file sizes and faster loading speeds. The script that converts materials is also no longer required, so I've removed it.

Unused unwrap cache (due to the import mode being Static Lightmaps) was also removed, as well as specular map textures which Godot doesn't use. If we enable lightmaps later, we can commit the unwrap cache but we should wait until we actually need it.

[Calinou]

Thanks! Congratulations for your first merged pull request 🎉

[franciscod]

Thank you!

For reference, this implements the first three GPU Benchmarks from #36:

• 🟩GPU🟩 [GI,Lighting,Effects,AA,DOF]: Sponza with Ambient Light: Sponza only lit by ambient light.
• 🟩GPU🟩 [Lighting]: Sponza with directional light: Sponza lit with a directional light and shadows.
• 🟩GPU🟩 [Lighting]: Sponza with omni lights: Sponza lit by several omni lights casting shadows.