a11y: Move relationset updating to new vfunc
a11y: Move relationset updating to new vfunc

This way, we don't create lots of cell accessibles when creating the
first one (because surely one is the parent/child of another who again
is a parent/child of another who again....)

Lyude/gtk-,jigpu/gtk,alexlarsson/gtk,Sidnioulz/SandboxGtk,chergert/gtk,Adamovskiy/gtk,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,ahodesuka/gtk,Adamovskiy/gtk,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,jessevdk/gtk,jadahl/gtk,Lyude/gtk-,msteinert/gtk,ahodesuka/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,msteinert/gtk,chergert/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,ahodesuka/gtk,grubersjoe/adwaita,Lyude/gtk-,jigpu/gtk,alexlarsson/gtk,Lyude/gtk-,chergert/gtk,msteinert/gtk,davidgumberg/gtk,jadahl/gtk,davidgumberg/gtk,Lyude/gtk-,ahodesuka/gtk,chergert/gtk,jadahl/gtk,jessevdk/gtk,jadahl/gtk,jessevdk/gtk,jessevdk/gtk,chergert/gtk,Lyude/gtk-,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,chergert/gtk,jessevdk/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,ahodesuka/gtk,jigpu/gtk,ahodesuka/gtk,jadahl/gtk,alexlarsson/gtk,msteinert/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,chergert/gtk,msteinert/gtk,jessevdk/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,Sidnioulz/SandboxGtk,davidgumberg/gtk,davidgumberg/gtk,jessevdk/gtk,Adamovskiy/gtk,grubersjoe/adwaita,msteinert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk