Add file validator for out of the box solution.

What steps will reproduce the problem?

What is the expected result?

What do you get instead?

Additional info

Q	A
Version	1.0.?
PHP version
Operating system

Add validator for UploadFile and SplFileInfo.

[samdark]

1. It should work w/ UploadedFileInterface from PSR-7.
2. May support multiple uploads for the same field.

[samdark]

Since there's no PSR-7 dependency in this package, it might be worth having it elsewhere.