Move IoUtils#deleteContents from CorePlatformApi set to framework

As a part of internal core libraries cleanup move usages of
IoUtils#deleteContents from CorePlatformApi set to framework.

Bug: 154796679
Test: m update-api
Merged-In: If7037029026b6753ab64be09aa52c40e04d5c7b1
Change-Id: If7037029026b6753ab64be09aa52c40e04d5c7b1

tests/utils/testutils/java/com/android/internal/util/test/FsUtil.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.internal.util.test;
+
+import java.io.File;
+
+public class FsUtil {
+
+    /**
+     * Deletes all files under a given directory. Deliberately ignores errors, on the assumption
+     * that test cleanup is only supposed to be best-effort.
+     *
+     * @param dir directory to clear its contents
+     */
+    public static void deleteContents(File dir) {
+        File[] files = dir.listFiles();
+        if (files != null) {
+            for (File file : files) {
+                if (file.isDirectory()) {
+                    deleteContents(file);
+                }
+                file.delete();
+            }
+        }
+    }
+}