MultipleFileUploadStatusItem: add event param to onReadFail, onReadFinished, onReadStarted and onReadSuccess callbacks. It should be first parameter.

[wise-king-sullyman]

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[wise-king-sullyman]

With the current structure of MultipleFileUpload consumers would need to pass the DropEvent in to MultipleFileUploadStatusItem, then it would just get returned to them in these callbacks.

Closing because of the above mentioned reasons combined with the fact that we expect to combine single and multiple file upload in the not distant future.