Summary: Adds additional functional interfaces for primitives and "Bi" (two operand). Adds utility extension methods. Includes some name changes for existing functional interfaces per EG decisions.
Reviewed-by: briangoetz, darcy, chegar, dholmes

8005311: Add Scalable Updatable Variables, DoubleAccumulator, DoubleAdder, LongAccumulator, LongAdder
Reviewed-by: chegar, darcy, goetz