Fix initialization of mutable types
# What does this PR do?

This PR fixes the initialization of mutable types for Swin Transformer, SegFormer and BEiT (as pointed out by @FrancescoSaverioZuppichini in #15277).

It also fixes a small docs issue for Swin Transformer.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15365). All of your documentation changes will be reflected on that endpoint.<|||||>This is present in many more configurations, so if we decide to switch it should be for all of them and not only for three configs.

Having a default for a mutable parameter is dangerous when the function mutates the parameter, which is not the case for our config inits, it's merely stored. I don't think we need to switch to `None`, which would result in the signatures in the doc being less complete.<|||||>I'm also not convinced it's super important as these are lookup values, but if you feel strongly a simpler way of doing this is to switch everything tu tuples, which are immutable. It keeps the arguments in the docstrings as well and can be converted to lists quite easily.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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