Update solval in src/mip/HighsCutGeneration.cpp

[fwesselm]

• A variable may be complemented here, but its solution value is not updated accordingly.
• Also, cut generation is currently implemented twice (additional copy for conflict generation). I added a single utility for this, which simplifies the code.
• The effect on overall performance (in terms of geometric means) is small. However, a handful of long-running MIPs cannot be solved to optimality within 2 hours anymore (on Linux), because a different code path is taken.