Add an option to `HfArgumentParser.parse_{dict,json_file}` to raise an Exception when there extra keys
I added an option to `HfArgumentParser.parse_{dict,json_file}` to raise an Exception when there extra keys. The option is off by default, for backward compatibility.

For users of these functions, misspelled or incorrect keys in the parsed files/dicts could lead to hard-to-find errors, like putting `batch_size` in your config and wondering why the Trainer is using a different one, because the actual name is `per_device_train_batch_size`. The option will output a very similar error message to the normal argparse.


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