This adds the boundary_falloff_type and boundary_offset to control how the
falloff of the Boundary Brush is applied.
Boundary Origin Offset is the same concept as the Pose Origin offset in
the Pose Brush. It is a multiplier that adds extra length to the brush
radius to locate the deformation pivot further from the boundary without
affecting the falloff.
The Falloff type includes Constant (previous default), brush radius, loop
and loop and invert. Loop and Loop and Invert can be used to create
deformation patterns in a mesh.