[vector-api] Only hit-detect visible features

Previously the hit detection code used the renderedExtent_ at replay time. This made it possible to hit-detect features that weren't visible/rendered on the map. This change makes things more consistent, by only hit-detecting features that are visible on the map.

This follows up on https://github.com/openlayers/ol3/issues/1436#issuecomment-31525147.