Blender Git Loki

Sculpt: Use constraints in cloth deform brushes

Previously, deform brushes were modifying the final positions in the
simulation directly, which was causing all sorts of artifacts in the
deformed area and problems with other features of the solver.
Now these brushes deform a separate array of positions and the solver
adds constraints to them, so the real vertices are moved when solving
the constraints. This prevents those artifacts and gives the brush a
much better behavior.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8424