GPULightmapper: do not smoothen position

[williamd67]

Smoothen position caused positions to move outside their triangle which caused
side-effects as rays from those positions intersected with triangles which
could not be reached from the original triangle.

[williamd67]

This PR fixes the artifact of strange blob that was mentioned in #51638.

After removing the smoothening of positions:

@JFonS, do you know the situation this smoothening was needed, or do you have a scene that needed it, as I may have broken that case and like to look into it so can fix it (maybe in another way without this side-effect). Thanks.

[JFonS]

If this section of code is causing artifacts then there's probably something wrong with it, but ideally we should try to keep it.

I did not write the original implementation of the GPU lightmapper, I just worked on some fixes and improvements, but I'm pretty sure this section is here to improve shadow termination. The same article is referenced somewhere in this file, but I believe this section is what Juan referenced while working on this feature. It has a good explanation of the problem and the solution we are (in theory, at least) implementing.

[williamd67]

Thanks @JFonS for the reference. I will investigate:

1. if there is an issue with the implementation (or if this a known side-effect)
2. the reference and determine if we could implement it without side-effects (if 1. seems to be correct)

I propose not to merge this PR till the investigation is concluded.

EDIT: the code is indeed needed for shadow termination so should not be removed. I will close this PR and create a new one with a correct name and implementation.

[williamd67]

This PR is replaced by #53322 is the solution of this PR is incorrect.