Earliest phone I can think of, off hand, that has it is the Google Pixel XL from 2016. Latest phone, of course, being the ROG 3 which recently got it through an OTA update. Even the Moto Z3 play has it, as do a fair number of other high to low end Android devices of all sorts.
It sure would do wonders for our battery health and life, create a longer shelf life and be such a great surprise. I believe this is the number one missing feature from our gaming phone. Consider that it has a non removable battery and is running a power hungry SOC, with an added 2.8 ghz frequency. Well, that and a landscape usb port, but let's not get off track into the impossible/physical.
I know the mobile department for the RP2 is bare bones as of late, and we thank you for the security updates and mobile cortex work.
I've looked for kernel patch code to apply it myself, but have come up empty handed thus far. It's out there though, as some custom kernels have it too.
A few examples: Kirisakura Kernel from OnePlus and Universal Kernel from Redmi 8. It is also in the Oxygen OS kernel repo, but scrubbing that for code I've never seen before and reverse engineering it, is not my cup of tea.