PR #11761: [GPU] Support nccl comm splitting in multiprocess mode
PR #11761: [GPU] Support nccl comm splitting in multiprocess mode

Imported from GitHub PR https://github.com/openxla/xla/pull/11761

Currently `--xla_gpu_enable_nccl_comm_splitting` is a no-op unless using single process mode. This PR allows it to work in multiprocess mode by removing the IsLocal check and fixing the key in the rank -> comm map which was causing the following error:
```
7:  Communicator for rank 1 not found in a NCCL clique devices=[3,7]; stream=0
5: E0403 15:37:24.104311 3871038 pjrt_stream_executor_client.cc:2809] Execution of replica 0 failed: INTERNAL: Communicator for rank 1 not found in a NCCL clique devices=[1,5]; stream=0
6: E0403 15:37:24.104477 3870182 pjrt_stream_executor_client.cc:2809] Execution of replica 0 failed: INTERNAL: Communicator for rank 1 not found in a NCCL clique devices=[2,6]; stream=0
4: E0403 15:37:24.105872 3871021 pjrt_stream_executor_client.cc:2809] Execution of replica 0 failed: INTERNAL: Communicator for rank 1 not found in a NCCL clique devices=[0,4]; stream=0
```
Copybara import of the project:

--
c77ed08f77e252a5068a23d02555ffa765913d42 by Trevor Morris <tmorris@nvidia.com>:

Enable nccl comm split for multiprocess mode

Merging this change closes #11761

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/11761 from trevor-m:tmorris-multiprocess-split c77ed08f77e252a5068a23d02555ffa765913d42
