[Neuron] Add Neuron device communicator for vLLM v1

[gnovack]

This PR is part of the effort to support vLLM v1 architecture on the neuron platform (see #11152). This change adds a device communicator class for the neuron backend using torch_xla.

Neuron-specific test cases are added to tests/neuron and are based on the existing distributed comms tests in tests/distributed/test_comm_ops.py

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[mergify[bot]]

This pull request has merge conflicts that must be resolved before it can be merged. Please rebase the PR, @gnovack.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[simon-mo]

@youkaichao @robertgshaw2-redhat would be great to get an understanding whether fits architecturally