Windows: Implement QPlatformTheme::WheelScrollLines.

Obtain the system setting via SystemParametersInfo(),
amending fac71528cc.

Task-number: QTBUG-49561
Change-Id: Ie7a956fdc6b175ad09356949645c1e8937053abd
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/plugins/platforms/windows/qwindowstheme.cpp

@@ -393,6 +393,8 @@ QVariant QWindowsTheme::themeHint(ThemeHint hint) const
         return QVariant(booleanSystemParametersInfo(SPI_GETSNAPTODEFBUTTON, false));
     case ContextMenuOnMouseRelease:
         return QVariant(true);
+    case WheelScrollLines:
+        return dWordSystemParametersInfo(SPI_GETWHEELSCROLLLINES, 3);
     default:
         break;
     }