Add a compact bitmask PrimitiveType for efficiently storing data masks

[arteymix]

This would be an alternative to the PrimitiveType.BOOLEAN that would make storing masks for single-cell data considerably more efficient.

[arteymix]

Java has a native implementation for that https://docs.oracle.com/javase/8/docs/api/java/util/BitSet.html.

[ppavlidis]

Gemma 2 disposition: Won't fix