Add the ability to insert delegate map entries via handles (#1371)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1371

For some backends, it is more efficient to provide debug handles than Nodes.

This enables the ability to do so

Reviewed By: tarun292

Differential Revision: D51871752

fbshipit-source-id: da65d40fd2c35e239f3818ee7d87af6dba19c1b4