Allow additional id values to be passed to the File component's aria-describedby

[maurercw]

As a simpler approach to #250, I was trying to add the validation message myself with an InlineAlert, but I'm not able to properly handle the aria-describedby since it's already being set for the file name part. If you allow additional ids to be passed in for the aria-describedby, it might make for an easier implementation.