Allow MpDeviceLoader to shard dictionaries of tensor #10115

Job	Run time
get-torch-commit	3s
Build XLA CUDA plugin / build	3m 23s
Build PyTorch/XLA / build	3m 16s
Build PyTorch with CUDA / build	1s
CPU tests	1s
GPU tests	1s
Build docs	1s
GPU tests requiring torch CUDA	1s
TPU tests	1s
	6m 48s

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