Multiple files upload not possible

[medienbaecker]

Describe the bug
While it's mentioned in the upload action docs, I'm pretty sure it's impossible to upload more than one file or use a file input with the multiple attribute in the first place.

If I'm not mistaken, there are two things that can't possibly work:

1. To upload multiple files we need to add [] to the input name, but Uniform can't handle this (?)
2. The file validator can't possible handle multiple files. It will always fail since there's an additional array around this array with the error key.

To Reproduce
Steps to reproduce the behavior:

1. Add a file input with multiple to your form.
2. Try to upload multiple files
3. See error

Was this ever possible/tested or am I missing something?