refactor(algebra/category/Group/basic): Avoid data shuffle in `mul_equiv.to_Group_iso` (#12407)
refactor(algebra/category/Group/basic): Avoid data shuffle in `mul_equiv.to_Group_iso` (#12407)

Change the definition of `mul_equiv.to_Group_iso` from `{X Y : Type*} [group X] [group Y] (e : X ≃* Y) : Group.of X ≅ Group.of Y` to `{X Y : Group} (e : X ≃* Y) : X ≅ Y`. Not making `X` and `Y` into `Group`s on the fly avoids rebundling them when they already are `Group`s, which breaks definitional equality.





leanprover-community/mathlib,leanprover-community/mathlib