Fix mixed smoothed and non-smoothed face normals computation for CSG shapes

[MythTitans]

When computing smoothed normals on CSG shapes, the normals from all the faces sharing a vertex are averaged together to compute the smoothed "shared" normal between the faces.

I don't think the behavior is correct, because it means that even faces that are not smoothed participate to the computation of their smooth neighbor's faces.

The problem is particularly visible when substracting a sphere or a torus from a box, at the edge between them :

Before

After

and also on the cylinder which has a strange shading (and a small glitch is visible at the bottom left) :

Before

After

This is related to some comments in #49800.

Bugsquad edit:

• Fixes CSGCylinder3D has incorrect normals compared to the CylinderMesh primitive #49800

[akien-mga]

CC @hoontee

[hoontee]

Fixes #49800.

[akien-mga]

After fixing the style issue, be sure to rebase to squash the commits into one (see https://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#the-interactive-rebase).

[Calinou]

By the way, this likely supersedes godotengine/godot-proposals#1862. Great work 🙂

[MythTitans]

@akien-mga Thanks, I'll read and try that

[hoontee]

By the way, this likely supersedes godotengine/godot-proposals#1862. Great work 🙂

No, there are still instances where angle based smoothing would be appreciable. Note the odd lighting on the cylinder due to a lack of hard edges around the sphere negation:

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.5.

[akien-mga]

Cherry-picked for 3.4.4.