This commit adds a simple facility for converting component rates at
surface conditions to voidage rates at reservoir conditions. It is
intentionally limited in scope and meant to be employed only in the
context of class FullyImplicitBlackoilSolver<> or something very
similar. In particular, class SurfaceToReservoirVoidage<> assumes
that it will be used to compute conversion coefficients for
component rates to voidage rates, and that those coefficients will
typically be entered into the coefficient matrix of a linearised
residual.
Add a trivial test just to demonstrate the setup and calling
process. This is not a feature or correctness test.
