Add descriptive convertJsonToPdx(..) conversion method.

Add protected jsonFormatterFromJson(..) method to encapsulate the invocation of the JSONFormatter.fromJSON(..) method.

Add wrap(:PdxInstance) method to wrap the PdxInstance generated from JSON in a new instance of PdxInstanceWrapper.

Resolves gh-67.

apache-geode-extensions/src/main/java/org/springframework/geode/pdx/PdxInstanceWrapper.java

@@ -118,7 +118,7 @@ public class PdxInstanceWrapper implements PdxInstance, Sendable {
 	 * never {@literal null}.
 	 * @see org.apache.geode.pdx.PdxInstance
 	 */
-	protected PdxInstance getDelegate() {
+	public PdxInstance getDelegate() {
 		return this.delegate;
 	}