Use bindings for anchors
Anchor margins were set by initial properties, which is not a binding, meaning that when the panel form factor changes, the margins won't be updated.
Use proper bindings instead.
BUG: 489492 FIXED-IN: 6.1.4
(cherry picked from commit 04c6e0f2)
6204ddf3 Use bindings for anchors
Co-authored-by: Marco Martin notmart@gmail.com