Implement copy_, fill_, and ones_like for Nested Tensors backends (#87728)
Summary: This diff implements copy_ in order to allow pinned memory transfers for nested tensors, as well as fill_ and ones_like, to test whether nested tensors can be created with other factory functions.
Test Plan: Pass all CI and sandcastle jobs.
Reviewed By: mikekgfb
Differential Revision: D40689594
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87728
Approved by: https://github.com/cpuhrsch
Author
Antoni Viros i Martin
