[Experimental] Gaussian splatting rendering in Blender 5.3 alpha

Gaussian splatting rendering technique landed in Blender main branch after many months of hard work as of 2026/09/17
It is not guaranteed to be in 5.3, since the code is still work in progress and things may change after public scrutiny and found bugs, but it looks promising and on track, if things go well to be in 5.3

This makes rendering spatial point cloud data better, since the splats make the points look more solid and continuous.

It currently works for PLY and SPZ file formats.

Work and discussion: https://projects.blender.org/blender/blender/issues/159470