Fix file upload progress bar

Split from #2587755: AJAX error when using progress bar on file field widget

When uploadprogress is available, Drupal.file.progressBar temporarily changes the name of the hidden field that contains the key for pecl (from filename[0][UPLOAD_IDENTIFIER] to UPLOAD_IDENTIFIER) or apc uploadprogress (from filename[0][APC_UPLOAD_PROGRESS] to APC_UPLOAD_PROGRESS). However, the jQuery.form plugin starts submitting the form before the field name is changed. We need to ensure that the name change is done before the jQuery.form plugin submits the form. The patch for this is ready to be reviewed. A full explanation of all the approaches we tried is in comment #70.

D7 post data

------WebKitFormBoundary4d4zgU831PUSggVA
Content-Disposition: form-data; name="UPLOAD_IDENTIFIER"

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with

D8 post data

------WebKitFormBoundaryctCyV2fneyPxBbKl
Content-Disposition: form-data; name="field_file[0][UPLOAD_IDENTIFIER]"

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