Trimmed IGES and STEP Internal Structures Export

[Ayush Jain]

Hello,

I'm finding that `ComputeFeaMesh` with FEA_STEP_FILE_NAME and FEA_IGES_FILE_NAME does not write any output file on macOS ARM64, Python 3.11, OpenVSP 3.50.2. (upgraded due to update to this capability) The docstrings describe these as "FEA Mesh trimmed STEP/IGES export type". FEA_STL_FILE_NAME works correctly with the same setup. EXPORT_STEP_STRUCTURE / EXPORT_IGES_STRUCTURE via ExportFile do write files but produce untrimmed planes, not the trimmed intersection cutouts that FEA_STEP_FILE_NAME / FEA_IGES_FILE_NAME are supposed to provide.

I can produce what I want from the GUI through the FEA Structures -> Intersect Only -> Export CAD.

I'm doing something similar to this

```
import openvsp as vsp
from pathlib import Path

vsp.VSPRenew()
wing_id = vsp.AddGeom("WING")
vsp.Update()
si = vsp.AddFeaStruct(wing_id)
vsp.Update()

for label, file_type, path in [
    ("STL",  vsp.FEA_STL_FILE_NAME,  Path("/tmp/wing.stl")),
    ("STEP", vsp.FEA_STEP_FILE_NAME, Path("/tmp/wing.stp")),
    ("IGES", vsp.FEA_IGES_FILE_NAME, Path("/tmp/wing.igs")),
]:
    vsp.SetFeaMeshFileName(wing_id, si, file_type, str(path))
    vsp.ComputeFeaMesh(wing_id, si, file_type)
    print(f"{label}:", f"{path.stat().st_size//1024} KB" if path.exists() else "NOT FOUND")
```

Any advice greatly appreciated. Thank you!

[Rob McDonald]

Instead of calling ComputeFeaMesh, I recommend you use the Analysis Manager with the 'FeaMeshAnalysis' analysis.

Long ago, every different analysis in OpenVSP had its own API.  ComputeFeaMesh is from that time.

Then, the AnalysisMgr was added to provide a common API for OpenVSP analyses.  The old way was not removed, but it is better to use the new way.

Rob

[ayush...@gmail.com]

Thank you!