This commit adds logic and backing storage in the SegmentState to
provide the segment level summary vectors
- SDENx -- Phase density of phase 'x' (O, G, W)
- SDENM -- Mixture density without flowing fraction exponents
- SMDEN -- Mixture density with flowing fraction exponents
We defer the calculation of SDENM and, especially, SMDEN, to the
MultisegmentWellSegments class since this class maintains the
current flowing fractions.
In particular, calculate segment flow velocities, segment holdup
fractions, and segment phase viscosities when updating the well
state. This is purely for reporting purposes and does not affect
the multisegmented model.
