8177960: Deprecate the Swing Motif Look and Feel and document it as unsupported on macOS

Reviewed-by: psadhukhan, prr

src/java.desktop/share/classes/com/sun/java/swing/plaf/motif/MotifLookAndFeel.java

@@ -60,8 +60,12 @@ import sun.awt.OSInfo;
  * long term persistence.
  *
  * @author unattributed
+ * @deprecated The Motif Look and Feel is deprecated with the intent to remove
+ *             it in some future release. It is recommended to use
+ *             {@link javax.swing.plaf.metal.MetalLookAndFeel} instead.
  */
 @SuppressWarnings("serial") // Superclass is not serializable across versions
+@Deprecated(since="13", forRemoval=true)
 public class MotifLookAndFeel extends BasicLookAndFeel
 {
     public String getName() {

src/java.desktop/unix/classes/sun/awt/X11/XAWTLookAndFeel.java

@@ -38,7 +38,7 @@ import javax.swing.plaf.basic.BasicBorders;
 import com.sun.java.swing.plaf.motif.*;
 import sun.awt.X11.XComponentPeer;
 
-@SuppressWarnings("serial") // JDK-implementation class
+@SuppressWarnings({"serial", "removal"}) // JDK-implementation class
 class XAWTLookAndFeel extends MotifLookAndFeel {
 
     /**