Shallow augmentation not working for nested relations

[goellner]

Bug Description

If you have extended shallowAugmentedArrayKeys like the following snippet, the augmentation does not work on the "link_internal_related" field, which is a replicator with an entry field in it. "link_internal_related" returns the full dataset of the entry and not only the keys specified in shallowAugmentedArrayKeys;

class CustomEntry extends Entry
{
    protected function shallowAugmentedArrayKeys()
    {
        return [
            'id',
            'title',
            'url',
            'permalink',
            'api_url',
            'link_internal_related',
        ];
    }
}

How to Reproduce

1. Extend shallowAugmentedArrayKeys with fields, that contain relations.
2. Open the API url of the entry, to see the data
3. The link_internal_related data contains all the data of the related entry instead of the keys specified in shallowAugmentedArrayKeys

Extra Detail

Shared with Jesse in Discord

Environment

Statamic version: 3.0.0 and up I guess
Tested with 3.0.2, 3.0.6 and 3.0.23

[goellner]

I have forked the starter kit and recreated the bug: https://github.com/goellner/starter-kit-cool-writings

I tried to have meaningful commits, so you can see every step that leads to this bug.