Is there a voltage regulator IC that takes PWM input?
I doubt such a device exists. A PWM signal as such is not a good start to generate a stable output voltage with as little ripple as possible. The regulator would require a filter with a rather large capacitor (I guess you want to draw some current from it), which will need to be external anyway. It wouldn't save you any space in any case.
If your PWM signal is to supply power, and not just a voltage, you'll have to provide a power driver, since PWM signals usually only provide a voltage.