Improve window placement (Maximizing) on Xwayland
x11window: Calculate the native floor from the beginning of the output
If this function is useful to make sure we are properly aligned with the output's pixels, we should start with the output's 0, otherwise we'll be carrying over the rounding errors increasingly as our workspace grows.
Marking as the bug closed because it fixes the problem for me, I can't be sure it will get fixed for the author, although I'm sure it will help.