Ability to fillet onto arcs

[merlin-mecado]

It seems that currently, one can only fillet onto edges of two straight lines, and an error (The Zoo engine cannot handle this 3D subtraction yet. Please report this as an issue
Edge cut failed
startProfile()) gets raised when you try to fillet onto an extrusion created by an arc. Other CAD softwares have no issue making these fillets, so would be nice to have them cleanly integrated.