Retain child item identity when using a NameMangler

PR #376 caused every child to be recreated on reload, whereas the
intent is to retain the object identity.

Author: Vlatombe

src/main/java/com/cloudbees/hudson/plugins/folder/AbstractFolder.java

@@ -365,8 +365,8 @@ public static <K, V extends TopLevelItem> Map<K, V> loadChildren(AbstractFolder<
             V itemFromDir;
             V item;
             String name;
-            item = itemFromDir = byDirName.get(childName);
             var legacyName = subdir.getName();
+            item = itemFromDir = byDirName.get(legacyName);
             try {
                 if (item == null) {
                     XmlFile xmlFile = Items.getConfigFile(subdir);

src/test/java/com/cloudbees/hudson/plugins/folder/ChildNameGeneratorAltTest.java

@@ -49,6 +49,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Set;
@@ -69,6 +70,7 @@
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 
 
 /**
@@ -120,8 +122,16 @@ public void evaluate() throws Throwable {
                 assertThat("Item loaded from disk", i, instanceOf(ComputedFolderImpl.class));
                 instance = (ComputedFolderImpl) i;
                 checkComputedFolder(instance, 0);
+                var items = new ArrayList<>(instance.getItems());
                 instance.doReload();
                 checkComputedFolder(instance, 0);
+                var newItems = new ArrayList<>(instance.getItems());
+                // Check child items identity is preserved
+                assertThat("Items are the same", items, is(newItems));
+                for (int k = 0; k < items.size(); k++) {
+                    assertSame("Individual items must be the same", items.get(k), newItems.get(k));
+                }
+
             }
         });
     }