[dtensor] updated api and doc

[FrankLeeeee]

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Fixed #3921

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This PR updated the API usage and documentation of DTensor.

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[github-actions]

The code coverage for the changed files is 87%.

Click me to view the complete report

Name                                                      Stmts   Miss  Cover
-----------------------------------------------------------------------------
colossalai/device/device_mesh.py                            143      6    96%
colossalai/lazy/lazy_init.py                                299     40    87%
colossalai/tensor/comm_spec.py                              253     93    63%
colossalai/tensor/d_tensor/__init__.py                        3      0   100%
colossalai/tensor/d_tensor/comm_spec.py                     151     35    77%
colossalai/tensor/d_tensor/d_tensor.py                       67     11    84%
colossalai/tensor/d_tensor/layout.py                         38      1    97%
colossalai/tensor/d_tensor/layout_converter.py              202     13    94%
colossalai/tensor/d_tensor/sharding_spec.py                 105     14    87%
tests/test_device/test_device_mesh.py                        11      1    91%
tests/test_device/test_init_logical_pg.py                    27      1    96%
tests/test_lazy/lazy_init_utils.py                           71     14    80%
tests/test_lazy/test_distribute.py                           73      3    96%
tests/test_tensor/test_dtensor/test_comm_spec.py             81      1    99%
tests/test_tensor/test_dtensor/test_dtensor.py               67      5    93%
tests/test_tensor/test_dtensor/test_layout_converter.py      91      1    99%
tests/test_tensor/test_shape_consistency.py                  50      2    96%
tests/test_tensor/test_sharded_linear.py                    130      1    99%
tests/test_tensor/test_sharding_spec.py                      13      1    92%
-----------------------------------------------------------------------------
TOTAL                                                      1875    243    87%