When using the Voxel Remesh operator, there are two possible sources of
crashes currently:
* TBB task stealing in nested parallel loops with thread local data
* Null dereference of PBVH data when pushing sculpt undo steps
To fix the former issue, this commit guards the
`threading::parallel_for` internal function with
`threading::isolate_task` to prevent possible task stealing and
corruption of the thread local data.
Additionally, it has the effect of fixing debug asserts inside
`array_utils::gather` due to the this task stealing.
To fix the latter issue, this commit adds a call to
`BKE_sculpt_update_object_for_edit` to ensure that this data is
populated.
Original PR: !129704
Pull Request: https://projects.blender.org/blender/blender/pulls/129823
Sean Kim
cbc33871c6