Move metadata util to a separate header for reuse (#4550)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4550

As titled.

imported-using-ghimport

Test Plan: Imported from OSS

Reviewed By: lucylq

Differential Revision: D60812259

Pulled By: larryliu0820

fbshipit-source-id: 196e3a3ef7660e70e733ecf36584debcc0c897b5