a11y: Only emit expandable/expanded for expander column
a11y: Only emit expandable/expanded for expander column

We don't want to emit state changes for all the cells in a row, just for
the cell in the expander column. It's the only one that reports EXPANDED
or EXPANDABLE states, after all.

Also, contains refactoring of the affected functions for all the special
cases.

https://bugzilla.gnome.org/show_bug.cgi?id=694059

bratsche/gtk-,Lyude/gtk-,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,bratsche/gtk-,jigpu/gtk,bratsche/gtk-,davidt/gtk,Adamovskiy/gtk,davidgumberg/gtk,Distrotech/gtk2,Adamovskiy/gtk,jessevdk/gtk,jessevdk/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,Lyude/gtk-,Sidnioulz/SandboxGtk,Distrotech/gtk2,alexlarsson/gtk,msteinert/gtk,ahodesuka/gtk,chergert/gtk,chergert/gtk,jessevdk/gtk,chergert/gtk,msteinert/gtk,jigpu/gtk,ahodesuka/gtk,alexlarsson/gtk,davidgumberg/gtk,davidt/gtk,Distrotech/gtk2,ebassi/gtk,Distrotech/gtk2,jadahl/gtk,msteinert/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,alexlarsson/gtk,grubersjoe/adwaita,jessevdk/gtk,Adamovskiy/gtk,Distrotech/gtk2,ebassi/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,davidt/gtk,chergert/gtk,davidgumberg/gtk,Adamovskiy/gtk,Lyude/gtk-,davidgumberg/gtk,jigpu/gtk,jessevdk/gtk,ahodesuka/gtk,jadahl/gtk,bratsche/gtk-,davidgumberg/gtk,Adamovskiy/gtk,ahodesuka/gtk,davidt/gtk,alexlarsson/gtk,ebassi/gtk,alexlarsson/gtk,jigpu/gtk,grubersjoe/adwaita,ebassi/gtk,jadahl/gtk,chergert/gtk,Adamovskiy/gtk,Lyude/gtk-,chergert/gtk,ebassi/gtk,Adamovskiy/gtk,jigpu/gtk,Lyude/gtk-,jigpu/gtk,alexlarsson/gtk,ahodesuka/gtk,jessevdk/gtk,jadahl/gtk,bratsche/gtk-,alexlarsson/gtk,grubersjoe/adwaita,davidt/gtk,grubersjoe/adwaita,ahodesuka/gtk,jadahl/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,ahodesuka/gtk,msteinert/gtk,ebassi/gtk,davidt/gtk,msteinert/gtk,jigpu/gtk,Lyude/gtk-,Distrotech/gtk2,jadahl/gtk,grubersjoe/adwaita,jadahl/gtk,Adamovskiy/gtk,msteinert/gtk,chergert/gtk,jessevdk/gtk,bratsche/gtk-,davidgumberg/gtk,grubersjoe/adwaita