Add "width gradient" similar to brush's color gradient

If you want to connect two lines of different colors and avoid sharp color shifts, you can use color gradient to smooth the transition.

But what about connecting two lines of different widths? Would be nice to have a similar function, but for kurbo's stroke. Maybe this could even work for dashes, where patterns would converge at the joint

(sorry if this is the wrong library for this issue, please let me know which would be the correct one)