This node is a bit of a weird case, because it uses the value stored in an
output socket as an input. So when we want to determine if the Dot
changed, we also have to check if the Normal output changed.
A cleaner solution would be to refactor this by either storing the normal
on the node directly (instead of in an output socket), or by exposing it
by a separate input. This refactor should be done separately though.
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