[unbloating] move pipeline utilities to pipeline_utils

[sayakpaul]

What does this PR do?

Move methods like calculate_shift(), retrieve_latents(), and retrieve_timesteps() to pipeline_utils.py to reduce a lot of LOC.

Didn't make these changes to the files under examples/community.

Note

I didn't start any deprecation for this because the respective scripts from which these methods are removed will anyway contain their imports.

[HuggingFaceDocBuilderDev]

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[JoeGaffney]

Nice, i do know there is a do repeat yourself ethos and I'm not a massive fan of overly DRY code with confusing abstractions.

But think in allot of cases lifting more of the common things out instead of the # Copied from makes allot more sense in readability. Especially as more and pipelines are sharing ideas from one another.

[sayakpaul]

Thanks @JoeGaffney! Yes, those will essentially be considered similar to how transformers does it (something like unpacking inheritance to not distort readability).

[DN6]

Looks good to me. cc: @yiyixuxu here too.