Fix SystemParameters.MenuDropAlignment's description (#8922)

#7920

Author: m2jean

xml/System.Windows/SystemParameters.xml

@@ -5411,7 +5411,7 @@
       <Docs>
         <summary>Gets a value indicating whether pop-up menus are left-aligned or right-aligned, relative to the corresponding menu item.</summary>
         <value>
-          <see langword="true" /> if left-aligned; otherwise, <see langword="false" />.</value>
+          <see langword="true" /> if right-aligned; otherwise, <see langword="false" />.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[