Summary

When waking from deep sleep, it could be helpful to know what pins triggered the wake up since the wake pins could be configured to multiple pins.

Based on work that @m-cas did in this PR - #15498.

Testing

Tested ESP32_GENERIC_C3 with:

import machine
import esp32
esp32.wake_on_gpio((machine.Pin(5),machine.Pin(2)), esp32.WAKEUP_ANY_HIGH)
machine.deepsleep()

After wakeup checked that machine.wake_pins() returned the correct pin that trigerred the wake.

Trade-offs and Alternatives

I decided to place the method in machine together with wake_reason, since it is feasible that other ports
will want the exact same interface.