Menu: Use disabled arrow icon if menu is disabled

Fixes #259

core/src/main/java/com/github/weisj/darklaf/ui/menu/DarkMenuUI.java

@@ -38,6 +38,7 @@ public class DarkMenuUI extends BasicMenuUI implements MenuItemUI {
     protected int acceleratorTextOffset;
     protected boolean useEvenHeight;
     protected Icon arrowIconHover;
+    protected Icon arrowIconDisabled;
     protected JMenu menu;
     protected MouseListener mouseListener;
 
@@ -107,6 +108,7 @@ public class DarkMenuUI extends BasicMenuUI implements MenuItemUI {
         acceleratorForeground = UIManager.getColor("Menu.foreground");
         acceleratorSelectionForeground = UIManager.getColor("Menu.selectionForeground");
         arrowIconHover = UIManager.getIcon("Menu.arrowHover.icon");
+        arrowIconDisabled = UIManager.getIcon("Menu.arrowDisabled.icon");
         useEvenHeight = !Boolean.TRUE.equals(UIManager.get(getPropertyPrefix() + ".evenHeight"));
         acceleratorTextOffset = UIManager.getInt(getPropertyPrefix() + ".acceleratorTextOffset");
     }
@@ -123,6 +125,8 @@ public class DarkMenuUI extends BasicMenuUI implements MenuItemUI {
     }
 
     protected Icon getArrowIcon() {
+        if (!menuItem.isEnabled())
+            return arrowIconDisabled;
         boolean hover =
                 menuItem.getModel().isArmed() || (menuItem instanceof JMenu && menuItem.getModel().isSelected());
         return hover ? arrowIconHover : arrowIcon;

core/src/main/resources/com/github/weisj/darklaf/ui/menuItem.properties

@@ -77,6 +77,7 @@ RadioButtonMenuItem.acceleratorTextOffset          = 10
 
 #Icons
 Menu.arrowIcon                                     = navigation/arrow/thick/arrowRight.svg[themed]
+Menu.arrowDisabled.icon                            = navigation/arrow/thick/arrowRightDisabled.svg[themed]
 Menu.arrowHover.icon                               = navigation/arrow/thick/arrowRightHover.svg[themed]
 Menu.checkIcon                                     = empty(0,0)
 MenuItem.checkIcon                                 = empty(0,0)