Refactor autoPyTorch/pipeline/components/preprocessing/tabular_preprocessing/XXX/__init__.py

[nabenabe0928]

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Since there are duplications in codes, it is better to unite them.
For more information, I added TODOs in coalescer/__init__.py

[ravinkohli]

It seems like this is a replica of #267. So I'll close that issue and lets carry it from here.