Refresh LineNumberRulerColumn on ZoomChange of canvas

This commit adds a listener for the ZoomChanged event to the canvas of a LineNumberRulerColumn. If the listener is notified of this event this means, that state, that differs over different zoom values, must be recalculated. Therefore the indentation are reset, when the event occurs.

Contributes to eclipse-platform/eclipse.platform.swt#62 and eclipse-platform/eclipse.platform.swt#131

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/LineNumberRulerColumn.java

@@ -616,6 +616,8 @@ public void addMouseListener(MouseListener listener) {
 			fCachedTextWidget= null;
 		});
 
+		fCanvas.addListener(SWT.ZoomChanged, e -> computeIndentations());
+
 		fMouseHandler= new MouseHandler();
 		fCanvas.addMouseListener(fMouseHandler);
 		fCanvas.addMouseMoveListener(fMouseHandler);