Add DDP NeighborLoader examples

[LukeLIN-web]

Since NeighborLoader is supported by pyg-lib. We could add an example in distributed_sampling_loader.py.
I refer #5340 (comment) to set kwargs = {'batch_size': 1024, 'num_workers': 0}

[rusty1s]

Thank you! Can we replace the existing example with NeighborLoader?

[LukeLIN-web]

Thank you! Can we replace the existing example with NeighborLoader?

Yes, we could replace the existing pytorch_geometric/examples/multi_gpu/distributed_sampling.py.
Do you mean I shouldn't change too many lines; Only replace the necessary lines of distributed_sampling.py?

[rusty1s]

Yes, since we want to fully replace NeighborSampler with NeighborLoader, I think just replacing the example would be best.

[codecov]

Codecov Report

Merging #6307 (3b24091) into master (cc2afb8) will not change coverage.
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  Files         381      381           
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  Hits        17990    17990           
  Misses       3276     3276           

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[LukeLIN-web]

Yes, since we want to fully replace NeighborSampler with NeighborLoader, I think just replacing the example would be best.

Thank you. I replaced the example and test epoch time, PyG2.2.0 spend half the epoch time than 2.1.0 so that I believe the code is correct.