[12.x] feat: Add current_page_url to Paginator

[mariomka]

Sometimes, it is useful to have the current page URL for the Paginator, for example, to customize how the pagination information is returned in the API resources collections:

class ApiResourceCollection extends AnonymousResourceCollection
{
    public function paginationInformation(Request $request, array $paginated, array $default): array
    {
        return [
            'links' => [
                'self' => $paginated['current_page_url'],
                'next' => $paginated['next_page_url'] ?? null,
            ],
        ];
    }
}

It simply adds a property to the toArray() method, so it shouldn't break anything.

[cosmastech]

I imagine that this is going to break a lot of unit tests for people who are asserting against the JSON structure without calling ->etc() [which I think is a best practice of writing tests against JSON responses, FWIW].

[fragkp]

True! @taylorotwell Please revisit this change, this might be a breaking change.