Incorrect PHPDoc for get_current_screen

[markauk]

The PHPDoc documentation for get_current_screen doesn't properly define the type of object which is returned. It should be:-

* @return object WP_Screen

Patch attached.

Obviously this doesn't make any difference to the running of the code, but will make life easier for anyone with IDE's which parse PHPDoc comments.

Since we can name the specific class it could be:

@return WP_Screen Current screen object

Yes! I was being unnecessarily frugal with words...

Patch updated.

The point was that you can omit 'object' and simply use the actual object WP_Screen as the type designator.

In [19942]:

Use class name for @return. props markuak, fixes #20063.