@type WP annotations for array/object shapes

[kkmuffme]

These are unfortunately also used in some hooks docs, e.g. pre_reschedule_event

@johnbillion you previously already implemented handling for those in https://github.com/php-stubs/wordpress-stubs/blob/master/src/WordPressTag.php and https://github.com/php-stubs/wordpress-stubs/blob/master/src/Visitor.php#L729

I'd prefer to not duplicate that code, however it first needs to be split out there (the getTypesAtLevel, isOptional,...) so that can be reused easily here.
Any takers for that @IanDelMar ?
Then we could add that package as a dependency here to reuse that easily.