Tapered extrudes accept profiles that mix lines and tangent arcs (slots, D-profiles, rounded rectangles): each arc keeps its centre and angles and its radius moves with the taper, so its side stays an exact cone; lines are offset and mitred. An arc meeting another edge at a corner is still refused. Un-ignores the #546 regression test. Fixes#546.
Co-authored-by: jonaswre <[email protected]>