Blender Git Loki

Geometry Nodes: Use multithreading for the curve to mesh node

This commit optimizes the node for the case where it works on many
splines by allowing it to generate mesh data from their combinations
in parallel. By itself, this made the node around twice as fast in my
test file with a result of 20 million vertices, around 600ms instead of
1.2s before.

That isn't actually a very good result; it reveals another bottleneck,
a single threaded loop over all face corners in the mesh normal
calculation code. As a simple change that might improve performance
in some situations, this commit moves normal calculation out of this
node, so at least the work isn't wasted if the mesh is changed later
on in the node tree anyway.