List all relationship field types

I’m trying to query all the relational/relationship field types that are used on the site. For instance, I use two: resource_links, quick_links, but I’m likely to add more. I’m trying to incorporate this as an array for a drop down menu to use with a shortcode in Visual composer. I use other field types, like basic text, etc, so I’d just want to list the field_name(s) of the relationship field types.

I hope that makes sense.

https://www.ads-software.com/plugins/advanced-custom-fields/