This commit introduces a new mode for calculating the positions and weights of the IK segments in the Pose Brush based on the Face Sets. The first segment of the chain will always include all face sets inside the brush radius and it will propagate until the boundary of the last face sets added in the flood fill. Then consecutive connected face sets are added to the chain until the chain length limit is reached or all face sets of the mesh are already part of the chain. This feature enables complete control over the pose brush origins in case that is needed. Also, with this mode, the user can have a library of base meshes with face sets already configured to get to the initial pose as fast as possible. Reviewed By: jbakker Differential Revision: https://developer.blender.org/D7235