Fix LaF Defaults internal action

This action obtain all keys using `UIManager.getDefaults().keys()`, that creates HashSet from entries, so hashcode value of JBColor is required. But there are also stored `JBColor.CACHED_NULL` values, that throw an exception when hashcode method is invoked. So, it is required to specify hashcode function for such marker objects.

GitOrigin-RevId: bc66322a58625bacc1f961581569decaf605bf2f

platform/util/ui/src/com/intellij/ui/JBColor.java

@@ -93,6 +93,11 @@ public class JBColor extends Color {
         return this == obj;
       }
 
+      @Override
+      public int hashCode() {
+        return name.hashCode();
+      }
+
       @Override
       public String toString() {
         return name;