[win32] different coordinate system strategie

This contributes extracts two different strategies to provide a consistent coordinate system in the win32 implemenentation for a single-zoom and a multi-zoom environment. The existing logic remains unchanged in this commit. It is only moved and consolidated in the new inner classes in Display

Contributes to eclipse-platform#62 and eclipse-platform#131

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

@@ -3970,7 +3970,9 @@ void subclass () {
 public Point toControl (int x, int y) {
 	checkWidget ();
 	int zoom = getZoom();
-	return DPIUtil.scaleDown(toControlInPixels(DPIUtil.scaleUp(x, zoom), DPIUtil.scaleUp(y, zoom)), zoom);
+	Point displayPointInPixels = getDisplay().translateToDisplayCoordinates(new Point(x, y), zoom);
+	final Point controlPointInPixels = toControlInPixels(displayPointInPixels.x, displayPointInPixels.y);
+	return DPIUtil.scaleDown(controlPointInPixels, zoom);
 }
 
 Point toControlInPixels (int x, int y) {
@@ -4003,9 +4005,7 @@ Point toControlInPixels (int x, int y) {
 public Point toControl (Point point) {
 	checkWidget ();
 	if (point == null) error (SWT.ERROR_NULL_ARGUMENT);
-	int zoom = getZoom();
-	point = DPIUtil.scaleUp(point, zoom);
-	return DPIUtil.scaleDown(toControlInPixels(point.x, point.y), zoom);
+	return toControl(point.x, point.y);
 }
 
 /**
@@ -4031,7 +4031,8 @@ public Point toControl (Point point) {
 public Point toDisplay (int x, int y) {
 	checkWidget ();
 	int zoom = getZoom();
-	return DPIUtil.scaleDown(toDisplayInPixels(DPIUtil.scaleUp(x, zoom), DPIUtil.scaleUp(y, zoom)), zoom);
+	Point displayPointInPixels = toDisplayInPixels(DPIUtil.scaleUp(x, zoom), DPIUtil.scaleUp(y, zoom));
+	return getDisplay().translateFromDisplayCoordinates(displayPointInPixels, zoom);
 }
 
 Point toDisplayInPixels (int x, int y) {
@@ -4064,9 +4065,7 @@ Point toDisplayInPixels (int x, int y) {
 public Point toDisplay (Point point) {
 	checkWidget ();
 	if (point == null) error (SWT.ERROR_NULL_ARGUMENT);
-	int zoom = getZoom();
-	point = DPIUtil.scaleUp(point, zoom);
-	return DPIUtil.scaleDown(toDisplayInPixels(point.x, point.y), zoom);
+	return toDisplay(point.x, point.y);
 }
 
 long topHandle () {