Update EntityContext.php

if you have this information in FormHelper than you can could add ['min' => 0] when 'unsigned' attributes is !empty() and input type is 'number' - I would like to do that but at the moment I think I can't.
Or is there any chance to overwrite the EntityContext class? Which I think could be useful too.

of course I could overwrite the _addDefaultContextProviders() method in FormHelper but this doesn't look like the perfect solution
The ArrayContext should also implement these keys so the two continue to match.