EditorZoom

Shared font-size bounds for a Prolog source editor's zoom controls (Ctrl/Cmd +/-/0, Ctrl/Cmd + wheel), so every toolkit (ide-swing's RSyntaxTextArea, ide-web's Ace) agrees on how far zooming is allowed to go, instead of each reimplementing its own (previously drifted: 8-48 vs. 8-40) clamp.