Fix LineNumberRuler glitch from incorrect listener order on zoom

This change ensures that zoom change events occur *after* all the
listeners have been executed in LineNumberRuler.

Previously, zoom changes triggered buffer image invalidation
prematurely, leading to multiple redundant resize events. This caused
incorrect top pixel calculations when the scrollbar was adjusted after
zoom, resulting in rendering glitches during redraws of line numbers.

By deferring the SWT.ZoomChanged event until all the listeners have
completed, we avoid early image invalidation. Now, the
redraw uses a correctly invalidated buffer image, and top pixel
calculations are accurate, eliminating rendering artifacts.

Tested by simulating zoom changes and full scroll-down scenarios—line
number ruler now renders consistently without glitches.

Author: ShahzaibIbrahim

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

@@ -618,11 +618,13 @@ public void addMouseListener(MouseListener listener) {
 		});
 
 		fCanvas.addListener(SWT.ZoomChanged, e -> {
-			computeIndentations();
-			if (fBuffer != null) {
-				fBuffer.dispose();
-				fBuffer= null;
-			}
+			Display.getDefault().asyncExec(() -> {
+				computeIndentations();
+				if (fBuffer != null) {
+					fBuffer.dispose();
+					fBuffer= null;
+				}
+			});
 		});
 
 		fMouseHandler= new MouseHandler();