This commit centralises the way we incorporate damping factors (item
10 of the GUIDERAT keyword) into the calculation of group/well guide
rates. In particular, we create a structure that manages both the
current and the previous (damped) guiderate values and ensures that
the new guiderate value is
GR_p = f*GR_p' + (1 - f)*GR_p^{n-1}
with GR_p' denoting the "raw" guiderate value calculated directly
from potential rates at the current timelevel (n). GR_p^{n-1} is
the damped-and previously used-guiderate value from timelevel n-1.
Finally 'f' denotes the damping factor. This is the same approach
used previously, but with some small changes to exclude zero-valued
guiderates.
We furthermore remove one of the early returns in GuideRate::get().
There is no need to return the nominated phase's guiderate value if
the model phase rate is very low and doing so produces incorrect
water guiderates for the OPL5 well in the MOD4_GRP test case.
7649df53a2