Zooming by mouse click/wheel and shortcut toggling from Fit/
Fill to 100% already centers the zoom to the current
cursor position.
This patch also centers the zoom on the cursor position for:
- triggering Fill zoom (⇧ middle click/⇧+F)
- shortcut zooming in/out (Ctrl++/Ctrl+-)
- shortcut zooming to 100% (if Actual Size shortcut set)