A few places already calculated vertex normals with better contextual
information to improve performance. To allow changing the storage of
vertex normals more (mostly for improved caching), change some code
from "get normals, set values, clear dirty flag" to "make vertex
normals data, give to mesh". This makes the API less awkward too,
since previously the "get for write" and "clear dirty" calls always
had to be separated.
Pull Request: https://projects.blender.org/blender/blender/pulls/110754
eabff37483