Will I be able to lock all cores on the stock heatsink and not thermal throttle? Ryzen 7 2700 in particular
What do you mean by lock all cores? Like you OC all of them and keep it that way?
In that case, you can in normal thermal conditions, but thermal throttle can still happen if your CPU overheats.
whatever amds equivalent to multicore enhancement
The 2700 stock cooler is the Wraith Spire, which is OK for stock and a bit of overclocking. If you really want to push the chip, I think you'll want an aftermarket cooler. Same comment goes for the 1st and 2nd gen Ryzens with the mediocre Stealth cooler. Ryzen 3rd gen operates a bit differently and you are generally better off letting the built in clock booster do its thing.