[SPARK-17800] Introduce InterfaceStability annotation

## What changes were proposed in this pull request?
This patch introduces three new annotations under InterfaceStability:
- Stable
- Evolving
- Unstable

This is inspired by Hadoop's InterfaceStability, and the first step towards switching over to a new API stability annotation framework.

## How was this patch tested?
N/A

Author: Reynold Xin <rxin@databricks.com>

Closes apache#15374 from rxin/SPARK-17800.

Author: rxin

common/tags/src/main/java/org/apache/spark/annotation/InterfaceStability.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.spark.annotation;
+
+import java.lang.annotation.Documented;
+
+/**
+ * Annotation to inform users of how much to rely on a particular package,
+ * class or method not changing over time.
+ */
+public class InterfaceStability {
+
+  /**
+   * Stable APIs that retain source and binary compatibility within a major release.
+   * These interfaces can change from one major release to another major release
+   * (e.g. from 1.0 to 2.0).
+   */
+  @Documented
+  public @interface Stable {};
+
+  /**
+   * APIs that are meant to evolve towards becoming stable APIs, but are not stable APIs yet.
+   * Evolving interfaces can change from one feature release to another release (i.e. 2.1 to 2.2).
+   */
+  @Documented
+  public @interface Evolving {};
+
+  /**
+   * Unstable APIs, with no guarantee on stability.
+   * Classes that are unannotated are considered Unstable.
+   */
+  @Documented
+  public @interface Unstable {};
+}