IssueTracker

There is currently no API support for supplying default arguments to a target destination, from within the action, according to the [NavActionBuilder class reference](https://developer.android.com/reference/kotlin/androidx/navigation/NavActionBuilder).

For example, if I had an action defined similarly to the following example:

```
fragment<MyFragment>("my_fragment_dest_id") {
   ...
   argument("my_arg") {
       type = NavType.StringType
   }
}
```

I would expect to be able to create an action to that destination that provides a default argument, like the following (or something similar).

```
action("my_action_id") {
   destinationId = "my_fragment_dest_id"
      argument("my_arg") {
        defaultValue = "action_provided_default_value"
      }
   }
}
```

This seems like something that would be important to keep in parity with the functionality provided by the XML navigation graph resource.