Investigate possibility of `Window.hasPrevious()`

[mp911de]

For scrolling across results, we already provide a hasNext indicator. It would be good to have a hasPrevious state as well.

For offset-based scrolling, we can get the information from the offset (e.g. a scroll that starts at offset 1 will not have a previous page). For keyset-scrolling, we would need to read from the current cursor and read another item more (two more in total) to determine a previous and next indicator).

[arturs678]

It seems sufficient to check the scrollPosition that was passed to the query. If the isInitial() method on the passed ScrollPosition returns false, we can assume that there is a previous window.