leftover MD-SS coupling tasks from #2705

[andrew-platt]

From PR #2705

TODO before release to main OpenFAST dev branch
These will be addressed in future PR's to the dev-cbind branch

• Add in coupling for currents
  • SeaState
• Add wave directional spreading into MoorDyn for WaterKin = 2 (SeaState inputs to the MoorDyn grid)
• C-bind pointer passing (@rafmudaf is leading this)
• Test implementation for accuracy
• Add regression test for water kinematics in MoorDyn, include example input files
• Docs update with new input file formats

[RyanDavies19]

@andrew-platt everything here is done except for the wave directional spreading