[ add ] `Relation.Binary.Morphism.Construct.On`

[jamesmckinna]

Given a Setoid/IsEquivalence bundle/structure on type B, and h : A → B, to construct

• _≈_ : Rel A _,
  by = B._≈_ on h
• isRelHomomorphism : IsRelHomomorphism _≈_ B._≈_ h,
  by isRelHomomorphism = record { cong = id }
• isRelMonomorphism : IsRelMonomorphism _≈_ B._≈_ h,
  by isRelMonomorphism = record { isRelHomomorphism = isRelHomomorphism; injective = id }

And... that's just about it!

Followup: extend this to Algebra.Morphism.Construct.On. cf. #2863