Description:
------------
https://3v4l.org/LKFbZ

and it's a problem for optional parameters:

Test script:
---------------
interface AAA{
    function method($x);
}

interface BBB extends AAA{
    function method($x, $y = null);
}

// this works correctly:
class AA_ implements AAA{
    function method($x){}
}
class BB_ extends AA_ implements BBB{
    function method($x, $y = null){}
}
(new BB_())->method(1, 1);

// this doesn't:
abstract class AAA_ implements AAA{}
abstract class BBB_ extends AAA_ implements BBB{}
// AAA::method is checked to be compatible against BBB::method,
// while it should happen the opposite