ADF: renaming an activity should update references

Finished pipeline activities can be referenced by subsequent activities where expressions are supported.

```

@activity('name of the activity that ran prior').output

```

Unfortunately, this reference is just a string. When the referenced activtiy is renamed, the reference is broken.

My workaround is using the JSON representation and do search & replace when renaming activites to make sure that I catch all the references.

From usability perspective this is horrible and should be done automatically.