[v6?] add phpdoc parser

[DerManoMann]

https://github.com/phpstan/phpdoc-parser

[DerManoMann]

Turns out to be more involved than expected. However, slow progress has been made.

[DerManoMann]

Ended up writing this :) https://github.com/DerManoMann/type-info-extras

Now thinking about if/how to support something similar for PHP < 8.2 - or not at all. Perhaps #1669 (v6) should go to PHP 8.2 directly, not 8.1.