Does fast charging shortens the battery life?

No, fast charging will not shorten battery life. The phone monitors the internal temperature and will slow charging if necessary to keep it in a safe range. Fast charging is only fast to 80% charge; above that it slows the charge rate to avoid overcharging, and shuts of charging entirely at 100% (which is actually slightly short of 100% to really be careful about overcharging. My wife uses a 7.5 watt Qi wireless charger and just leaves the phone on it when she's not using it and overnight. That's slightly faster than the cube the phone comes with (50% faster to 80%), but this approach means she always has sufficient charge on her phone.

For major brand portable electronics this is how it works in general. It is carefully designed.