Because php supports doc comments on class constants, I believe it would also
make sense to support them on enum cases.
I don't have strong opinions about whether attributes should be moved to be the
last element or whether the doc comment should go after the attribute,
but the ast will likely change again before php 8.1 is stable.
So far, all attributes are the last ast child node.
I didn't notice that doc comments weren't implemented due to
https://github.com/php/php-src/pull/6489 being a large change.
https://wiki.php.net/rfc/enumerations
did not mention whether or not doc comments were meant to be supported
