Fixed more cases where attributes weren't being reinitialized
on switching PBVH mode:
* When PBVH_GRIDS and PBVH_BMESH force attributes into simple
array mode they no longer override simple_array in the
SculptAttributeParams parameters, instead they set a field
in SculptAttribute itself. Thus if the attribute is
reinitialized in another mode it won't retain the simple_array
parameter.
* sculpt_attribute_ensure_ex now calls sculpt_attr_update if
the attribute already exists.
* Fixed a bug from a couple commits ago that set
SculptAttribute.data_for_bmesh wrong.
This commit replaces the `Mesh_Runtime` struct embedded in `Mesh`
with `blender::bke::MeshRuntime`. This has quite a few benefits:
- It's possible to use C++ types like `std::mutex`, `Array`,
`BitVector`, etc. more easily
- Meshes saved in files are slightly smaller
- Copying and writing meshes is a bit more obvious without
clearing of runtime data, etc.
The first is by far the most important. It will allows us to avoid a
bunch of manual memory management boilerplate that is error-prone and
annoying. It should also simplify future CoW improvements for runtime
data.
This patch doesn't change anything besides changing `mesh.runtime.data`
to `mesh.runtime->data`. The cleanups above will happen separately.
Differential Revision: https://developer.blender.org/D16180
