change signature of map_impl (#1580)

Summary:
X-link: https://github.com/pytorch/pytorch/pull/117161

Pull Request resolved: https://github.com/pytorch/executorch/pull/1580

This PR changes the schema of map_impl from map_impl(f, num_mapped, *operands) to map_impl(f, mapped_args: Tuple, moperands: Tuple). This is to prepare for turning on dynamo for eager mode map, where we want to get rid of the num_mapped scalar.

Reviewed By: angelayi

Differential Revision: D52495413

fbshipit-source-id: 3f99074d3ab4a8badae3cc72e7422482837e255a