Blender Git Loki

Sculpt: use dynamic scheduling and chunk size 1 for multithreading

This is under the assumptions that each node has enough work to avoid
the threading overhead, while also having a possible variable amount of
work. For example most of the vertices being masked or outside of the
brush radius.

Improves performance by about 10% for tools like mesh filter on an
entire 3 million poly mesh, tested on a quad core.

Ref T68873