feat(data/equiv/basic): quot_equiv_of_quot(')
feat(data/equiv/basic): quot_equiv_of_quot(')

quot_equiv_of_quot matches matches the existing subtype_equiv_of_subtype,
but quot_equiv_of_quot' is useful in practice and this definition is careful
to use eq.rec only in proofs.

leanprover-community/mathlib,leanprover-community/mathlib