Polymorphic field should override dashboard selection from Associative

Created by: monkbroc

Currently Polymorphic is only an alias for Associative.

Associative#associated_dashboard uses the attribute name to select the correct dashboard.

In Polymorphic this leads to a uninitialized constant error when calling field.display_associated_resource during the render of app/views/fields/polymorphic/_index.html.erb

For a polymorphic relation, the correct dashboard should be taken from the class of the associated object if it exists.

My workaround right now is:

<% if field.data %>
  <%= link_to(
    "#{field.data.class.name}Dashboard".constantize.new.display_resource(field.data),
    polymorphic_path([:admin, field.data])
  ) %>
<% end %>

Do you agree with the approach? Is there a better way to get the associated dashboard name?

I can clean this up and make a PR for this.