As mentioned in new code comments, the auto smooth behavior in 4.0 was
to skip sharp angle tagging when the evaluated mesh had custom normals.
There was already a check for custom normals on the original mesh (we
can't access the evaluated mesh from versioning code). But that didn't
handle cases where custom normals were created by modifiers (the normal
edit and weighted normal modifiers). Now skip adding the new modifier
when those modifiers come last in the stack. Alternatively we could
check if they existed in the stack at all, but that seems a bit more
risky.
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