diviner: Atomize using PHP-Parser
Summary:
This allows Diviner to support atomizing PHP source files that use
features of newer versions of PHP.
Ref T16289
Test Plan:
* (Optional) Edit source files to use new PHP features (enums, union types)
* Run `./bin/diviner generate --clean`
* Look at the generated documention on http://phorge.localhost/book/dev/ of the file modified
Reviewers: O1 Blessed Committers, aklapper
Reviewed By: O1 Blessed Committers, aklapper
Subscribers: aklapper, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16289
Differential Revision: https://we.phorge.it/D26755