TSL: Introduce RaymarchingBox and raymarchingTexture3D

[sunag]

Related issue: #28418

Description

Introduce RaymarchingBox( steps, function ), this makes the API cleaner and raymarched with textures3d() can be used on any material more easily since it is now a node.

VolumeNodeMaterial could be discontinued after this PR but I'll probably keep it after a review for volumetric fog implementation. https://x.com/sea3dformat/status/1887405202774302835

RaymarchingBox( steps, ( { positionRay } ) => {

	const sample = texture3D( positionRay.add( 0.5 ) ).r;

	// ...

} );