texthandle: Track parent scrollable adjustments
texthandle: Track parent scrollable adjustments

This makes sure texthandles follow the parent if it is contained within a
GtkScrollable.

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