[win32] fix getting checkbox size from OS

This commit fixes fetching the checkbox size for custom drawn checkbox buttons. Instead of using the zoom adjusted by the swt.autoScale setting the native zoom is used. This is neccessary, because the checkbox will be drawn by the OS and therefore is matching the native zoom as well.

Fixes #1573

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

@@ -1311,7 +1311,7 @@ private int getCheckboxTextOffset(long hdc) {
 	SIZE size = new SIZE();
 
 	if (OS.IsAppThemed ()) {
-		OS.GetThemePartSize(display.hButtonTheme(getZoom()), hdc, OS.BP_CHECKBOX, OS.CBS_UNCHECKEDNORMAL, null, OS.TS_TRUE, size);
+		OS.GetThemePartSize(display.hButtonTheme(nativeZoom), hdc, OS.BP_CHECKBOX, OS.CBS_UNCHECKEDNORMAL, null, OS.TS_TRUE, size);
 		result += size.cx;
 	} else {
 		result += DPIUtil.scaleUp(13, nativeZoom);