[WIP] duplicate JOIN statement searching on multiple has_one though association

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original issue description:

Is this expected?

class Children < ActiveRecord::Base
  belongs_to :parent
  has_one :a_ancestor, through: :parent
  has_one :b_ancestor, through: :parent
  has_one :c_ancestor, through: :parent
end

class Parent < ActiveRecord::Base
  belongs_to :a_ancestor
  belongs_to :b_ancestor
  belongs_to :c_ancestor
end

class AAncestor < ActiveRecord::Base; end
class BAncestor < ActiveRecord::Base; end
class CAncestor < ActiveRecord::Base; end

Children.ransack(
  a_ancestor_id_eq: 1,
  b_ancestor_id_eq: 1,
  c_ancestor_id_eq: 1,
).result.to_sql

# => LEFT OUTER JOINs `parents` 3 times

Here's executable test of the issue

https://gist.github.com/Liooo/ea4629204f7f3233633125e5f134b574

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Additional instructions:

Determine if this is a problem and if so then create a failing PR in one comment and fixes in the next commit

Fixes #986

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