Before #108014, toggling "Auto Smooth" was an easy way to disable
evaluation of custom normals and face corner normals for faster
viewport playback performance. Now that corner normals are calculated
automatically as necessary, it's helpful to still have a way to disable
expensive normal computation for faster playback.
This commit adds a "Normals" scene simplify setting. To avoid a bunch
of complexity, it just influences which normals are requested from the
object by viewport rendering. In my tests, skipping calculating at
least doubled viewport FPS in a few test files with a large mesh with
custom normals. This works well because normals are cached and lazily
calculated.
Pull Request: https://projects.blender.org/blender/blender/pulls/113975
912c4c60d8