Description:
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Date interval calculation is has changed in 8.1 and the new calculation is incorrect.

8.0: https://3v4l.org/8g4NB#v8.0.8
8.1: https://3v4l.org/8g4NB/rfc#vgit.master

This seems similar to https://bugs.php.net/bug.php?id=80998

Test script:
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<?php

$time = '2000-01-01 00:00:00.000000';
$tz_aus = new DateTimeZone('Australia/Sydney');
$tz_us = new DateTimeZone('America/Los_Angeles');
$auz = new DateTime($time, $tz_aus);
$us = new DateTime($time, $tz_us);

$diff = $auz->diff($us);
// Should output int(19)
var_dump($diff->h);

Expected result:
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It should output:
int(19)

Actual result:
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int(0)