[Files] Clearer user on-screen message for File Upload Assignment type

[curtain]

For the file upload assignment type, if one uploads a file that does not fit the instructor defined file type restrictions (like a pdf when only doc/docx is accepted) Canvas returns a non-helpful error message.

It would be an improvement if it had a more user-helpful error message. Maybe something like, "Incorrect file type uploaded. Please see assignment details for file type information" or something like that.

This impacts students ability to complete the assignment in a timely manner or creates more questions for the instructors or 1st tier support.