[UX] disable "upload" button on file widget until file has been selected

I experience this UX problem a lot with new Drupal / Backdrop users. When presented with a file field on a form, they click the upload button before selecting a file, expecting the upload button is step 1 of the process and not step 2.

I think it might help if the upload button were disabled (or invisible?) until the user had selected a file. Here is a Drupal project that does exactly that: https://www.drupal.org/sandbox/clivelinsell/1587560