Expose MappingReader and MappingWriter

Jenkins Blue Ocean made interesting design choices relating github-api interactions.

They mostly reused the existing API and OM, but in a few places they chose to
implement their own object mapping independent of this project. This is fine
as long as nothing in this project ever changes, including internals such
as ObjectMapper configuration or behavior.

Recent release have made changes to those internals which break assumptions made
in Blue Ocean.

This change exposes this project's MappingReader and MappingWriter to allow
for a fix to Blue Ocean requiring only minimal changes.

This doesn't prevent future changes from breaking Blue Ocean but at least makes
them much less likely.

Author: bitwiseman

src/main/java/org/kohsuke/github/GitHub.java

@@ -23,6 +23,8 @@
  */
 package org.kohsuke.github;
 
+import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.infradna.tool.bridge_method_injector.WithBridgeMethods;
 
 import java.io.*;
@@ -1190,6 +1192,33 @@ public Reader renderMarkdown(String text) throws IOException {
                 "UTF-8");
     }
 
+    /**
+     * Gets an {@link ObjectWriter}. Do not use this method.
+     *
+     * @return an {@link ObjectWriter} instance that can be further configured.
+     * @deprecated Provided for backward compatibility with projects that did their own jackson mapping of this
+     *             project's data objects, such as Jenkins Blue Ocean.
+     */
+    @Deprecated
+    @Nonnull
+    public static ObjectWriter getMappingObjectWriter() {
+        return GitHubClient.getMappingObjectWriter();
+    }
+
+    /**
+     * Do not use this method. Objects mapped using the reader returned from this method will have minimal data mapped
+     * into them and not be fully functional. Use at your own risk.
+     *
+     * @return an {@link ObjectReader} instance that can be further configured.
+     * @deprecated Provided for backward compatibility with projects that did their own jackson mapping of this
+     *             project's data objects, such as Jenkins Blue Ocean.
+     */
+    @Deprecated
+    @Nonnull
+    public static ObjectReader getMappingObjectReader() {
+        return GitHubClient.getMappingObjectReader(GitHub.offline());
+    }
+
     @Nonnull
     GitHubClient getClient() {
         return client;