Add focusRectSizeFactor parameter for rectangle focus shape (like focusCircleRadiusFactor for circular). Default value should be 1.

At the moment, this can only be done through the XML (fastScrollEnabled), but often we want to enable/disable according to, for example, how many items there are in the list. So it would be good to add a property on the recyclerview for this.

Similarly, for other XML-only attributes.