[directory-upload] HTMLInputElement.getFilesAndDirectories should not throw (#20)

HTMLInputElement.getFilesAndDirectories should reject the returned Promise with InvalidStateError rather than throwing that error. Throwing makes writing code that calls that Promise returning methods messy because then()'ing becomes more difficult, especially if you want processing of the 'then' chain to handle the error and continue.

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Reply to this email directly or view it on GitHub:
https://github.com/WICG/directory-upload/issues/20