Update the ProcessFunction::getResult method to return the _result type instead of a general TBase

Author: CoolTomatos

lib/java/src/main/java/org/apache/thrift/ProcessFunction.java

@@ -83,7 +83,7 @@ protected boolean rethrowUnhandledExceptions() {
 
   public abstract boolean isOneway();
 
-  public abstract TBase<?, ?> getResult(I iface, T args) throws TException;
+  public abstract A getResult(I iface, T args) throws TException;
 
   public abstract T getEmptyArgsInstance();