Use portrait mode and disable rotation by default
As discussed with @devinlin and @bribbers, it would probably be useful to have portrait mode by default in Plasma Mobile and disable rotation by default. The user could enable rotation manually by pulling the menu from the tap and tapping on rotation.
Current behavior:
Rotation is on by default, and oftentimes it boots into landscape mode or has glitches related to switching between both (sometimes even leading to the black screen with white text on it saying it crashed etc -> #321). And switching happens too easily/unexpectedly currently by rotating the phone, we don't have any threshold there to figure out if the user actually intended to switch to landscape.
Tested with postmarketOS on OnePlus 6T.