Make size_dict conversion logs clearer

[amyeroberts]

What does this PR do?

• Tidies up logic for converting size parameter to the expected dictionary format for image processors.
• Adds param_name as a flag so logs reflect the variable being updated e.g. crop_size versus size

Address part of #20185 - trying to make the logs clearer.

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[amyeroberts]

@sgugger @patrickvonplaten The quickest and easiest remedy I had was adding a param_name flag for the get_size_dict function. This way, if an image processor has both size and crop_size variables being updated, the logs reflect the parameter being changed. However, it's a bit of a dirty trick. LMK if you have an alternative suggestion.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[sgugger]

Thanks for cleaning this up!

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[patrickvonplaten]

Thanks!