Previously, when evaluated on the face corner domain, the normal input
node just returned the face normals, as if the mesh was completely flat
shaded. This ignores face and edge smoothness, and custom face corner
normals. In the past couple years the expected behavior of accessing
normals has become much clearer and this behavior is clearly a mistake
in retrospect.
This commit exposes the same face corner normals used everywhere else
in Blender when the node is evaluated on the corner domain. The old
behavior is accessible with a node property in the sidebar. There is
versioning so old files have the property set and get the same results.
This is split from !132583.
Pull Request: https://projects.blender.org/blender/blender/pulls/133340
b36eb69038