MD: User-specified external forces and translational damping for MoorDyn point, rod, and body objects

[luwang00]

This PR is ready to be merged.

Feature or improvement description
This PR adds user-specified external forces (constant) and translational linear and quadratic damping coefficients to MoorDyn point, rod, and body objects.

A new optional input file section called EXTERNAL LOADS is added to the MoorDyn input file for these purposes, so no change to existing input files is necessary. Below is an example of the new optional MoorDyn input file section.

---------------------- EXTERNAL LOADS --------------------------------
ID    Object          Fext             Blin          Bquad         CSys
(#)   (name)           (N)            (Ns/m)       (Ns^2/m^2)      (-)
 1    Body1        0.0|0.0|0.0     0.0|0.0|0.0     0.0|0.0|0.0      G
 2    Body1        0.0|0.0|0.0     0.0|0.0|0.0     0.0|0.0|0.0      L
 3    Point1       0.0|0.0|0.0     0.0|0.0|0.0     0.0|0.0|0.0      -
 4    Rod1         0.0|0.0|0.0     0.0|0.0         0.0|0.0          -

For BODY, the force and damping are applied at the body reference point in the global earth-fixed coordinate system if CSys is G for global or in the local body-fixed coordinate system if CSys is L for local. CSys can only be G or L for BODY.

For POINT, the force and damping are applied at the point location in the global earth-fixed coordinate system always. CSys should be -. Otherwise, a warning message with explanation will be shown.

For ROD, the force is applied at the rod end A in the earth-fixed coordinate system always. Only two linear and two quadratic damping coefficients can be specified for rods. The first one is for the transverse direction, and the second one is for the axial/tangential direction. The damping force is always evaluated in the body-fixed system. CSys should be -. Otherwise, a warning message with explanation will be shown. Note that this new implementation serves as an extension and replacement of PR #2342.

This PR also addresses issue #2565.

The new feature and implementation are finalized after consulting with @RyanDavies19 and @mattEhall.

Jointly developed with @RyanDavies19.

Impacted areas of the software
MoorDyn

Test results, if applicable
No changes to existing input files or test results. Added a new MoorDyn module regression test md_BdyExtLdDmpg with external loads and damping on a body object.

[andrew-platt]

• Updates to regression tests -- make sure to merge that into r-test dev