Fix Volumetric Fog VoxelGI updates

[bitsawer]

• Fixes Volumetric fog with VoxelGI weird behavior depending on camera position #85765

The problem was that when VoxelGI volumes became visible in the camera or leave it, the active VoxelGI culling results were not updated to volumetric fog uniform sets. The updates only happened when toggling the enviroment off and on or resizing the windows, which forces a full update. More specifically, this volumetric fog uniform update code needs to be re-run every time when VoxelGI culling results change:

godot/servers/rendering/renderer_rd/environment/fog.cpp

Lines 857 to 864 in b94eb58

	RD::Uniform u;
	u.uniform_type = RD::UNIFORM_TYPE_TEXTURE;
	u.binding = 12;
	for (int i = 0; i < RendererRD::GI::MAX_VOXEL_GI_INSTANCES; i++) {
	u.append_id(p_settings.rbgi->voxel_gi_textures[i]);
	}
	uniforms.push_back(u);
	copy_uniforms.push_back(u);

There are few similar volumetric fog update issues that I think might be caused by similar missing uniform (or some other) update, for example #83990 (the same workaround also works there, turning environment off and on or resizing the window).

The Volumetric Fog and VoxelGI interactions and uniform set handling received some work in #76437, #76550 and #77703, so it could be useful to get some feedback from @RandomShaper here. There might be a more elegant or efficient way to implement the update notifying logic, especially if there are other cases like #83990 that need to be also handled in the future, but this should fix the immediate problem.

[Calinou]

Tested locally, it works as expected. I've also tested a larger scene with a single VoxelGI node and it still renders correctly.

Before

simplescreenrecorder-2023-12-11_11.40.20.mp4

After (this PR)

simplescreenrecorder-2023-12-11_11.45.19.mp4

[BastiaanOlij]

The heart of the fix seems correct, right now we detect whether the uniform is null or dependencies have been updated, but then only create the uniform set if it's null.
I'm guessing at some point in time we would have freed the uniform set maybe?
But freeing the uniform set before (re)creating it makes sense.

Setting dependencies as changed while we update those seems sound to me as well.

[akien-mga]

@bitsawer Could you rebase this PR just to make sure it still passes CI a few months later?

Edit: Done myself.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.2.2.