[Problem] There is no 3D PDF export option

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Problem description

There is no way to directly export into a 3D PDF and keep tree structure, materials and custom views.
https://helpx.adobe.com/acrobat/using/adding-3d-models-pdfs-acrobat.html

3D related file types to be used in 3D PDF are Universal 3D (.U3D) files (https://en.wikipedia.org/wiki/Universal_3D)

Related issue for import of these files:
- https://github.com/FreeCAD/FreeCAD/issues/6090

There is a commercial app for conversion, which uses Brep, not tesselated solids: https://tetra4d.com/tetra-4d-converter/
Shouldn't it be easier for FreeCAD to use BReps instead of tesselating them? This would be much more powerful.

Sample files: https://tetra4d.com/pdf-samples/ (scroll down to converted files)

### Full version info

```shell
OS: Windows 11 build 22631
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.36277 (Git)
Build type: Release
Branch: main
Hash: 9e1903d46112b3660bf10c6a4537d728101d560b
Python 3.10.13, Qt 5.15.8, Coin 4.0.2, Vtk 9.2.6, OCC 7.6.3
Locale: German/Germany (de_DE)
Installed mods:
* 3DfindIT 1.2.0
* BIM 2021.12.0
* CfdOF 1.25.2
* CurvedShapes 1.0.5
* Curves 0.6.23
* Defeaturing 1.2.2
* fasteners 0.5.12
* FEMbyGEN 2.1.0
* freecad.gears 1.2.0
* freecad_metal_workbench 0.0.1
* OpenDark 2023.12.17
* sheetmetal 0.4.2
```

### Subproject(s) affected?

Core

### Anything else?

https://helpx.adobe.com/acrobat/using/displaying-3d-models-pdfs.html
https://helpx.adobe.com/acrobat/using/interacting-3d-models.html#interacting_with_3d_models
https://helpx.adobe.com/acrobat/using/measuring-3d-objects-pdfs.html#measuring_3d_objects_in_pdfs

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

Start by reviewing open pull request #23335 and the related import issue #6090; the payload names no source files or tests. Done means providing a 3D PDF export that preserves the model tree, materials, and custom views.

Written by the indexing model from the issue text.