changes to MappedExamplesIterable to resolve #7345

[vttrifonov]

modified MappedExamplesIterable and test_iterable_dataset.py::test_mapped_examples_iterable_with_indices

fix #7345

@lhoestq

[vttrifonov]

I noticed that Dataset.map has a more complex output depending on remove_columns. In particular this line removes columns from output if the input is being modified in place (i.e. input_columns = None). I tried to mimic this behaviour in MappedExamplesIterable by checking if the input and output point to the same dictionary object.

[HuggingFaceDocBuilderDev]

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[lhoestq]

looks good to me !

can you run make style to fix code formatting for the CI ?
edit: I also took the opportunity to fix an old bug at #7358

[lhoestq]

perfect !