fix: clear input value on clearFiles from imperative handle

[Steven7926]

Summary

A simple change that clears the input elements value in a file input component when the files state is cleared through the imperative handle.

First PR so any feedback would be greatly appreciated. Thanks!

Closes #3089

How To Test

1. Use the FileInput component with ref and custom handlers that has a "clear files" button. Story Book example: https://trussworks.github.io/react-uswds/?path=/story/components-file-input--with-ref-and-custom-handlers
2. Add a file to the FileInput component.
3. Clear the file using the clear files button.
4. Ensure the file clears.
5. Add a new file to the FileInput
6. Ensure the event is fired and the file i added properly to the component.