[executorch] Create target for named_data_map

Pull Request resolved: https://github.com/pytorch/executorch/pull/8110

named_data_map depends on tensor_layout, which depends on exec_lib.

Move it out from core, as we have a circular dep when exec_lib is part of core.

Also make TensorLayout::create return a const.
ghstack-source-id: 264157518

Differential Revision: [D68972364](https://our.internmc.facebook.com/intern/diff/D68972364/)

Co-authored-by: lucylq <lfq@meta.com>