Ubuntu 18.04: Put window into screen corner
Solution 1:
After writing the question, a similar one popped up: Resize 4 windows to occupy the screen without overlap on Ubuntu 18.04
The keyword was "tiling" and the GNOME extension ShellTile does exactly what I was looking for.
Solution 2:
GNOME Extension of preference for me is: Put Windows
It's supposed to be a replacement for the Unity functionality you mentioned.
Solution 3:
Use ShellTIle
First enable extensions with: (the prefix chrome is not related to chromium, it works on any window)
sudo apt install chrome-gnome-shell
Then go to ShellTIle
And click ON