feat: Add have_delegated_type matcher

[matsales28]

On this PR, we're adding the matcher for the delegated_type macro, which is basically a belongs_to polymorphic association where you define the possible classes the polymorphic relation can act as.

Currently, it is hard to check those possible classes as Rails does not expose them in any way, so we need to check if the methods for those classes are defined, which is not ideal.

class Vehicle < ActiveRecord::Base
  delegated_type :drivable, types: %w(Car Truck)
end

# Usage 
RSpec.describe Vehicle, type: :model do
 it { should have_delegated_type(:drivable) }
end

[matsales28]

This is not great, but currently, there's no way to check the types besides doing that. A PR was merged recently, adding a types method to the object, which will greatly simplify this check. I will update this method once it is released in Rails.

rails/rails#50662

[matsales28]

I'll wait to see what happens when running all the specs, but when the relation is polymorphic, the reflection.klass method raises an error. I found this while trying to create a spec to replicate a case where you have a polymorphic association or delegated_type one, but you also pass the scopes qualifier to that association. When trying to make a spec for that cause, I noticed this problem.

My solution was to return a valid ActiveRecord object(which in that case, I returned the subject itself) because this will be used only to grab the value of the where_values_hash in the ModelReflector#extract_relation_clause_from, which I think doesn't matter which model you're using to. But we can think on another solution here.

[vsppedro]

LGTM!