[win32] Forward ZoomChanged to all child widgets

This commit adds forwarding of a ZoomChanged events in the DPI change handler of Composite. With that all non top level widgets will notified about the ZoomChanged event in the win32 implementation so custom widgets can register listeners to react on that.

Contributes to #62 and #131

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/DPIZoomChangeRegistry.java

@@ -16,6 +16,7 @@
 import java.util.*;
 import java.util.Map.*;
 
+import org.eclipse.swt.*;
 import org.eclipse.swt.widgets.*;
 
 public class DPIZoomChangeRegistry {
@@ -54,6 +55,12 @@ public static void applyChange(Widget widget, int newZoom, float scalingFactor)
 				handler.handleDPIChange(widget, newZoom, scalingFactor);
 			}
 		}
+		Event event = new Event();
+		event.type = SWT.ZoomChanged;
+		event.widget = widget;
+		event.detail = newZoom;
+		event.doit = true;
+		widget.notifyListeners(SWT.ZoomChanged, event);
 	}
 
 	public static void registerHandler(DPIZoomChangeHandler zoomChangeVisitor, Class<? extends Widget> clazzToRegisterFor) {

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Control.java

@@ -4900,7 +4900,7 @@ LRESULT WM_DESTROY (long wParam, long lParam) {
 LRESULT WM_DPICHANGED (long wParam, long lParam) {
 	// Map DPI to Zoom and compare
 	int newNativeZoom = DPIUtil.mapDPIToZoom (OS.HIWORD (wParam));
-	int oldNativeZoom = getShell().nativeZoom;
+	int oldNativeZoom = nativeZoom;
 
 	// Throw the DPI change event if zoom value changes
 	if (newNativeZoom != oldNativeZoom) {
@@ -4914,7 +4914,8 @@ LRESULT WM_DPICHANGED (long wParam, long lParam) {
 			DPIUtil.setDeviceZoom (newNativeZoom);
 		}
 
-		notifyListeners(SWT.ZoomChanged, event);
+		float scalingFactor = 1f * DPIUtil.getZoomForAutoscaleProperty(newNativeZoom) / DPIUtil.getZoomForAutoscaleProperty(oldNativeZoom);
+		DPIZoomChangeRegistry.applyChange(this, newNativeZoom, scalingFactor);
 
 		if (getDisplay().isRescalingAtRuntime()) {
 			RECT rect = new RECT ();

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Shell.java

@@ -311,11 +311,6 @@ public Shell (Display display, int style) {
 
 	reskinWidget();
 	createWidget ();
-
-
-	if (getDisplay().isRescalingAtRuntime()) {
-		addListener(SWT.ZoomChanged, this::handleZoomEvent);
-	}
 }
 
 /**
@@ -2647,12 +2642,6 @@ LRESULT WM_WINDOWPOSCHANGING (long wParam, long lParam) {
 	return result;
 }
 
-private void handleZoomEvent(Event event) {
-	int newNativeZoom = event.detail;
-	float scalingFactor = 1f * DPIUtil.getZoomForAutoscaleProperty(newNativeZoom) / getZoom();
-	DPIZoomChangeRegistry.applyChange(this, newNativeZoom, scalingFactor);
-}
-
 private static void handleDPIChange(Widget widget, int newZoom, float scalingFactor) {
 	if (!(widget instanceof Shell shell)) {
 		return;