For `SubdivCCG`, replace the dynamic array-of-struct data with separate
arrays for positions, normals, and masks. This decreases memory
bandwidth requirements for loops that only access one of these arrays.
It also significantly simplifies data access, making it more similar
to mesh data where it can just be accessed with indices.
In a simple test this change speeds up the multires sculpt brush
benchmark by 32%. It also slightly reduced BVH build time by about 12%.
In practice this means completely replacing usage of `CCGElem` for
`SubdivCCG`. The struct is still used in the older subsurf baking code
though. Removing that is a much trickier task that doesn't have short
term benefits.
Part of #118145.
Pull Request: https://projects.blender.org/blender/blender/pulls/127262
1618448abd