Move FisheyeProjection to scene/graphics for shared use

[mvaligursky]

Move FisheyeProjection out of gsplat-unified into scene/graphics, since it is also used by skybox rendering.

Changes:

• Move fisheye-projection.js from src/scene/gsplat-unified/ to src/scene/graphics/
• Update imports in gsplat renderer and skybox

[willeastcott]

Doesn't this feel more like a Camera property?

[mvaligursky]

In a way, but only two systems honor it (unified gsplat & infinite skydome), nothing else. Geometry, particles, UI, debug lines ... , none of that.

[LeXXik]

Feels like a camera thingy, though

[mvaligursky]

Feels like a camera thingy, though

Might feel like it, but it's not :)
Even camera matrices are not updated to handle this in any way,
This is a custom implementation in two shaders.