Incorporate Task/Workflow context to input/output/export API on the DSL

After #863 we now need to incorporate this change to the DSL. So users can do:

```java
workflow().tasks(f -> f.callFn(fn -> fn.function(myfunction::doSomething).exportAs((WorkflowContext, TaskContext) -> myExporter::export))
```

Also, improve the shortcuts to something like:

```java
workflow().tasks(call(function(myFunction::doSomething).exportAs(myExporter::export))))
```