textview: make magnifier size dependent on text size
textview: make magnifier size dependent on text size

The magnifier is now set enough height to show the line being currently
manipulated, which makes it just big enough to show the layout height at
that size and magnification.

jigpu/gtk,Lyude/gtk-,jadahl/gtk,Lyude/gtk-,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,Lyude/gtk-,davidgumberg/gtk,davidgumberg/gtk,chergert/gtk,jadahl/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,chergert/gtk,Lyude/gtk-,Lyude/gtk-,chergert/gtk,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,chergert/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,Adamovskiy/gtk,chergert/gtk,davidgumberg/gtk,Adamovskiy/gtk,davidgumberg/gtk,grubersjoe/adwaita,ahodesuka/gtk,chergert/gtk,Adamovskiy/gtk,jigpu/gtk,alexlarsson/gtk,ahodesuka/gtk,jigpu/gtk,Adamovskiy/gtk,Adamovskiy/gtk,grubersjoe/adwaita,ahodesuka/gtk,Lyude/gtk-,jadahl/gtk,ahodesuka/gtk,grubersjoe/adwaita,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,Adamovskiy/gtk,davidgumberg/gtk,Lyude/gtk-,Adamovskiy/gtk,Adamovskiy/gtk,chergert/gtk,ahodesuka/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,jadahl/gtk,ahodesuka/gtk,grubersjoe/adwaita,jadahl/gtk