[shardformer] fix pipeline forward error if custom layer distribution is used

[insujang]

…distribution

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fixed #5187

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Built-in model polices use self.distribute_layers and self.get_stage_index in every place so that pipeline forward works properly when a custom policy overrides those functions.

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[flybird11111]

Thank you for your contribution.

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[insujang]

It seems tests even didn't run due to timeout. Any hint why?