Build a Collapsible React Native Header Bar

In this lesson we'll create a collapsible header bar. This technique is used to show additional information or actions but hide when the user scrolls to expose more of the information they are looking at. We'll use a combination of ScrollView, onScroll, and the Animated.event function to update our Animated.Value every time the user scrolls. Then with a series of interpolate calls we can define a scroll threshold to show/hide pieces of information, as well as shrink the fontSize of our title.