Fix GH-19406: Redeclaring a protected constant in a child class should work

[alexandre-daubois]

Fix #19406

The PR only focuses on constants, the other failing cases seem to be fixed already. I targeted 8.4 because of what's been mentioned in the issue.

[iluuu1994]

I don't think this is the right solution. It allows accessing protected constants on any "cousin" class. E.g.

class P {}

class C1 extends P {
    protected const C = 'C1';
}

class C2 extends P {
    public static function test() {
        var_dump(C1::C);
    }
}

C2::test();
// string(2) "C1"

The same does not apply to properties. Time complexity is also not great, as zend_check_protected() itself has two loops, giving us O(n²).