Major Description
Today we are using a LinkedHashMap to buffer doc-values updates in
BufferedUpdates. This on the one hand uses an Object based datastructure
and on the other requires re-encoding the data into a more compact representation
once the BufferedUpdates are frozen. This change uses a more compact represenation
for the updates already in the BufferedUpdates in a parallel-array like datastructure
that can be reused in FrozenBufferedDeletes. It also adds an much simpler to use
API to consume the updates and allows for internal memory optimization for common
case updates.
