Clear the Actions list through CakeTaskBuilder

### What You Are Seeing?
The only way to clear Actions from a `CakeTaskBuilder` is not cast its `ICakeTaskInfo` to `CakeTask`.

### What is Expected?
I need to clean the actions from a Task. I have the `CakeTaskBuilder` which builds that task. I expect to be able to clear `Actions` without casting to exact type.

```
CakeTaskBuilder exampleTaskBuilder = Task("Example.Task")
.Does(()=>
{
// Some code
});

((CakeTask)exampleTaskBuilder .Task).Actions.Clear();
```

Possible solutions came to my mind:
* `ICakeTaskInfo` might contains a List> Actions { get; } method
* Or a specific `ClearActions()` method to clean the actions list.
* If `ICakeTaskInfo` should be read-only then maybe the CakeTaskBuilder could have a funcion to clear the previously added tasks.

Start by tracing CakeTaskBuilder, ICakeTaskInfo, and CakeTask to understand how actions are stored and exposed. Decide on and implement an API that lets a builder clear previously added actions without casting, then verify that the resulting task has no actions and that existing behavior remains intact.

Written by the indexing model from the issue text.