Even the Cloth Brush grab works like a regular grab brush, it makes
sense to support spacing just in this brush in order to prevent creating
more brush steps that update the simulation. This way, it is possible to
create grab brushes that update the simulation constantly while grabbing
(using the dots stroke mode) or brushes that only update the simulation
when the cursor moves (using spacing).
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D8568
5aecc4b57b