Move the RDE PGP file encoding to a dedicated file

The "file encoding" saves the file + metadata (filename and modification) in a "blob" format that PGP knows how to read.

Merges the file-encoder creation between RyDE and Ghostryde.

The new file - RydeFileEncoding.java - is a merge of the removed functions in
Ghostryde.java and the RydePgpFileOutputStream.java.

This is one of a series of CLs - each merging a single "part" of the encoding.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205295756

javatests/google/registry/rde/RydeFileEncodingTest.java

@@ -0,0 +1,53 @@
+// Copyright 2018 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.rde;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.io.ByteStreams;
+import google.registry.testing.ShardableTestCase;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.OutputStream;
+import org.joda.time.DateTime;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public final class RydeFileEncodingTest extends ShardableTestCase {
+
+  @Test
+  public void testEncodeDecode() throws Exception {
+    byte[] expectedContent = "Testing 1, 2, 3".getBytes(UTF_8);
+    String expectedFilename = "myFile.txt";
+    DateTime expectedModified = DateTime.parse("2015-12-25T06:30:00.000Z");
+
+    ByteArrayOutputStream output = new ByteArrayOutputStream();
+    try (OutputStream encoder =
+        RydeFileEncoding.openPgpFileWriter(output, expectedFilename, expectedModified)) {
+      encoder.write(expectedContent);
+    }
+    byte[] encoded = output.toByteArray();
+
+    ByteArrayInputStream input = new ByteArrayInputStream(encoded);
+    try (RydeFileEncoding.PgpFileInputStream decoder = RydeFileEncoding.openPgpFileReader(input)) {
+      assertThat(decoder.getFilename()).isEqualTo(expectedFilename);
+      assertThat(decoder.getModified()).isEqualTo(expectedModified);
+      assertThat(ByteStreams.toByteArray(decoder)).isEqualTo(expectedContent);
+    }
+  }
+}