Description:
------------
IntlGregorianCalendar doesn't have constants from parent class.

See https://3v4l.org/N8Ets

Test script:
---------------
<?php

class Foo extends \IntlCalendar
{
    
}

$fooReflection = new \ReflectionClass(\Foo::class);
$intlGregorianCalendarReflection = new \ReflectionClass(\IntlGregorianCalendar::class);

printf("%d constants in %s, ", count($fooReflection->getConstants()), \Foo::class);
if ($fooReflection->getParentClass()) {
    printf("%s extends %s\n", Foo::class, $fooReflection->getParentClass()->getName());
}
printf("%d constants in %s, ", count($intlGregorianCalendarReflection->getConstants()), \IntlGregorianCalendar::class);
if ($intlGregorianCalendarReflection->getParentClass()) {
    printf("%s extends %s\n", \IntlGregorianCalendar::class, $intlGregorianCalendarReflection->getParentClass()->getName());
}
printf("%d constants in %s\n", count((new \ReflectionClass(\IntlCalendar::class))->getConstants()), \IntlCalendar::class);

Expected result:
----------------
39 constants in Foo, Foo extends IntlCalendar
39 constants in IntlGregorianCalendar, IntlGregorianCalendar extends IntlCalendar
39 constants in IntlCalendar

Actual result:
--------------
39 constants in Foo, Foo extends IntlCalendar
0 constants in IntlGregorianCalendar, IntlGregorianCalendar extends IntlCalendar
39 constants in IntlCalendar