Issue: https://github.com/php/php-src/issues/11448
Author: mvorisek
### Description
repro: https://3v4l.org/GhnO4new DateTime() can parse (as expected) any number of fractional seconds
but DateTime::createFromFormat can parse only 1-6 digits
I know the php cannot represent more fractionals seconds currently, but fractional seconds are more
or less a floating point and if more digits are present, they should be parsed and discarded.
### PHP Version
any
### Operating System
any