Improve CoreGenericClasses (#2402)
Improve CoreGenericClasses (#2402)

- general formatting
- Better definition for iterator class for `ArrayObject`
- Better definition for callable parameters to `ArrayObject`/`ArrayIterator` `uksort`/`uasort`
- Fixed signature for `ArrayIterator::current()`
- Fixed signature for `DOMNodeList::item()`
vimeo/psalm,vimeo/psalm