Add support for ListHeaderComponent as sticky header in SectionList

[sreuter]

Introduction

While FlatList supports defining the ListHeaderComponent sticky, it currently doesn't seem to be supported for SectionList.

Details

facebook/react-native#29547

Discussion points

Should we do this? Seems like low-hanging fruit as SectionList is built on top of FlatList.

[NickGerleman]

ListHeaderComponent is a prop on the underlying VirtualizedList, where there is logic to compute stickyHeaderIndicies` of the ScrollView with/without the header. This would need a new prop and logic there.