Implement elliptic curve divide point

[user202729]

Implement the notation E / P or E / (P, Q) where E is an elliptic curve and P, Q are points of E.

This is somewhat opinionated, but I think the notation is not uncommon in math text (except that there they write E / Φ where Φ is a subgroup of E, or E / ⟨P⟩, but the subgroup type is not implemented in Sage yet)

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