Faster RoaringBitmap Serialization with v0.8.0

RoaringBitmap 0.8.0 adds faster serde, but also requires us to change how we call the serde routines slightly to take advantage of it. This is probably a worthwhile optimization as the every shuffle map task with a large # of partitions generates these bitmaps, and the driver especially has to deserialize many of these messages.

See

• https://github.com/apache/spark/pull/24264#issuecomment-479675572
• https://github.com/RoaringBitmap/RoaringBitmap/pull/325
• https://github.com/RoaringBitmap/RoaringBitmap/issues/319