Allow AssignedParameters cop to handle assigned methods

Noticed an issue with `AssignedParameters` not handling assigned methods correctly when using `FixedIndentation` for assigned methods.

For example, on auto correct:

Before:

```
  customer = Customer.login!(
    id,
    request,
    other_val
  )
```

After:

```
  customer = Customer.login!(
    id,
                       request,
                       other_val
  )
```


I'm not sure if I've handled enough cases, this could probably do with more work, but thought i'd start the conversation here.