Add convenient alternate for Map.merge?

Maybe there should be an additional function:

let mergeSimple: (
  t<'k, 'v, 'id>,
  t<'k, 'v, 'id>,
  ('k, 'v, 'v2) => option<'v3>,
  ('k, 'v) => option<'v3>,
) => t<'k, 'v3, 'id>

?