st: Transition from `vertical` to `orientation` properties
This is a proposal to switch from vertical
to orientation
properties,
which would be consistent with Clutter/GTK.
It also affects BoxLayout
that is one of the most used containers,
so it would be quite intrusive (while trivial to adjust).
So far I haven't update any JS code, I will do that if we agree to move forward with this.
Includes !3613 (merged).