display: Fix problems when left-most monitor is rotated

When rotating the left-most monitor, we could end up with one
of two scenarios:
- Huge gap between monitor one and two when the left monitor is made
to be vertical
- Monitor two overlapping on top of monitor one when monitor is
back to being horizontal.

In addition to adding a bit more debug, we now take the old and new
rotation of monitor one into account when calculating the moving
screen edges.

https://bugzilla.gnome.org/show_bug.cgi?id=731166