Add OpenCascade shared-module

[hadess]

Currently used by 3 different modules (I'm attempting to package a 4th one, and there's a 5th archived one):
https://github.com/search?q=org%3Aflathub+opencascade&type=code

Some using the mirror git at https://github.com/Open-Cascade-SAS/OCCT, some use tarballs, some use the upstream git repo.

It also requires tcl, tk, freeimage, vtk, maybe rapidjson.

[hfiguiere]

FreeCAD use a patched version of opencascade as recommended by the maintainers.

[TuxPaulus]

This is a very good idea to add OCCT in shared-module.
Did you give up on this project?
This might be of interest to other OCCT clients that are not yet in FlatHub.
For example CAD-Query or even SALOME.