This implements transform modes for the transform tool and Elastic
Transform. This mode uses the Kelvinlets from elastic deform to apply
the transformation to the mesh, using the cursor radius to control the
elasticity falloff.
{F9269771}
In order for this to work, the transform tool uses incremental mode when
elastic transform is enabled. This allows to integrate the displacement of
the Kelvinet in multiple steps.
Review By: Sergey Sharbin & Daniel Bystedt & Julian Kaspar & Campbell
Barton
Differential Revision: https://developer.blender.org/D9653
Ref D15041
e90ba74d3e