add bunch of new java APIs: mostly stubs or copied from AOSP

Many of these classes are only needed to be subclassed by androidx
support library, which is used in many android apps

src/api-impl/android/database/DataSetObserver.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2007 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 android.database;
+
+/**
+ * Receives call backs when a data set has been changed, or made invalid. The typically data sets
+ * that are observed are {@link Cursor}s or {@link android.widget.Adapter}s.
+ * DataSetObserver must be implemented by objects which are added to a DataSetObservable.
+ */
+public abstract class DataSetObserver {
+	/**
+	 * This method is called when the entire data set has changed,
+	 * most likely through a call to {@link Cursor#requery()} on a {@link Cursor}.
+	 */
+	public void onChanged() {
+		// Do nothing
+	}
+
+	/**
+	 * This method is called when the entire data becomes invalid,
+	 * most likely through a call to {@link Cursor#deactivate()} or {@link Cursor#close()} on a
+	 * {@link Cursor}.
+	 */
+	public void onInvalidated() {
+		// Do nothing
+	}
+}