More power to the renderGeometryFunction

The geometry passed to the `renderGeometryFunction` is the simplified geometry, not the original feature geometry. This makes it impossible to do `===` comparisons of the passed geometry with a feature geometry, unless there was nothing to simplify for the geometry. Even if it was the original geometry, it would not give much of a context to decide whether a geometry should be rendered or not.

With the feature that the geometry belongs to as 2nd argument, application developers have more context. They can e.g. use the `renderGeometryFunction` to avoid rendering of features that are on a selection overlay, or rendering of features whose attributes match certain conditions.

The one thing I was not sure about when creating this pull request was whether there is a planned future use of the opaque data object that was passed to `ol.renderer.vector.renderFeature()`. The only object that was ever passed to that function was an `ol.Feature`, so I considered that `data` argument redundant and removed it in the process of changing the type of that object from `{Object}` to `{ol.Feature}`.