Improve static analysis for paginator items

[princejohnsantillan]

Currently when using PaginatedDataCollection the items() method does not define the item data type.

Example:

$paginatedData = ExampleData::collect($data, PaginatedDataCollection::class); 

foreach($paginatedData->items()->items() as $item)
{
  /*
   * Problem #1: $item here is mixed 😢
   * Problem #2: items() returning a Paginator isn't intuitive, I expected the actual items. 
   *   We end up needing to do ->items()->items()
   */
}

• I added @return Paginator<TKey, TValue> to help with static analysis and address problem 1
• Added data method instead of changing the items method to address problem 2