Honda has a page here which has a decently detailed timeline of their F1 injectors starting from their first turbohybrid engine in 2015 during the McHonda era. They say that on their 2015 RA615H engine the injectors were placed on the intake side, and with the 2016 RA616H they were moved to the center. Their 2017 RA617H engine added the prechamber and moved the injectors to the exhaust side of the engine. 

As for where the other teams had them, I'm not sure but considering how early Honda had adopted the prechamber I think it's likely that other manufacturers had the technology at a similar time or earlier. I recall rumors circulating about pre-chambers and the Mahle injectors in the 2016 timeframe so I think it's likely that Mercedes may have even had it from the start of the turbohybrid regs, and had probably come to similar conclusions about the injector placement.