APSK Modulation

I can’t find any reference to Amplitude Phase Shift Keying (APSK) in any
of the GNU Radio documentation. I did try searching for “generic
constellation” and got some hits, but I’m not sure if that’s the correct
route to take for this unique mod type. How would you recommend I
implement APSK (16-APSK specifically) modulation/demodulation in GNU
Radio?