Automatic normals

[janEntikan]

It would be nice if I didn't have to worry about geometry normals. Something along the lines of Geom.recalculate_normals()

Usecases:

• "I want to construct my own geometry but I don't know what "cross product" means."
• "This mesh is flat shaded but I want it smoothed"
• "This mesh is inside out because I inverted the scale, I need to flip all the normals"
• "The artist was tipsy and three triangles are inverted"

[janEntikan]

Blender has a function that does this seemingly perfectly. https://docs.blender.org/manual/en/latest/modeling/meshes/editing/mesh/normals.html#recalculate

[rdb]

Good idea, would go well hand-in-hand with #803