Non-editable prop collection items would always fall back to the slower
loop in `rna_raw_access`.
This patch changes `RNA_property_collection_raw_array` to only fail with
non-editable items when intending to set values, allowing for the faster
raw array access to occur when reading values in `rna_raw_access`.
This brings the Python API `bpy_prop_collection.foreach_get` performance
of `Mesh.vertex_normals`/`polygon_normals`/`corner_normals` up to the same
speed as generic `FLOAT_VECTOR` attributes with the same domains.
Given a mesh with 393216 corners:
Using `foreach_get` with the "vector" prop and a compatible buffer object:
- Corner vector attribute: ~0.9ms
- Corner normals (before): ~7.9ms
- Corner normals (after): ~0.9ms
Using `foreach_get` with the "vector" prop and a Python list:
- Corner vector attribute: ~11.0ms
- Corner normals (before): ~18.0ms
- Corner normals (after): ~11.0ms
Pull Request: https://projects.blender.org/blender/blender/pulls/114063
9956ef4622