[8.x] Add missing onLastPage to CursorPaginator

[rodrigopedra]

Closes #42296

As stated on issue #42296 the docs on CursorPaginator``s available methods states it has a onLastPagemethod, but the implementation of that method is missing onIlluminate\Pagination\CursorPaginator` and its parent abstract class.

This PR:

• Adds the missing onLastPage implementation to Illuminate\Pagination\CursorPaginator
• Adds a test case covering both onLastPage and onFirstPage

[rodrigopedra]

Actually docs on 8.x does not have onLastPage under "Cursor Paginator Instance Methods"

https://laravel.com/docs/8.x/pagination#cursor-paginator-instance-methods

The missing method is only on 9.x docs:

https://laravel.com/docs/9.x/pagination#cursor-paginator-instance-methods

So I am closing this and sending to 9.x