CGAL_Qt6 and CGAL_data Cmake components are not properly handled via Conan

[efifogel]

CGAL_Qt6 and CGAL_data Cmake components are not properly handled via Conan.

These components fail to install; so if, for example, you put CGAL::Data or CGAL::CGAL_Qt6 in the arguments of the Cmake target_link_libraries() command, you get an error message:

 CMake Error at src/libs/cgalpy/CMakeLists.txt:773 (target_link_libraries):
   Target "CGALPY" links to:
     CGAL::Data
   
   but the target was not found.  Possible reasons include:
     * There is a typo in the target name.
     * A find_package call is missing for an IMPORTED target.
     * An ALIAS target is missing.

If there are additional components, then I guess that they don't work either (e.g., CGAL::Eigen3_support).

Source Code

One way to reproduce with a single command, is to build a Python binding library from the https://[email protected]/taucgl/cgal-python-bindings.git repository:

pip install [--user] [--force-reinstall] git+https://[email protected]/taucgl/cgal-python-bindings.git@master

At the time this issue was filed, the command above worked (without CGAL_Qt6 and CGAL_data) under Ubuntu and Windows, but possibly failed under Macs (for reasons different than this bug). (It's possible that by the time you are reading this, these other problems are gone.)

Environment

• Operating system (Windows/Mac/Linux, 32/64 bits): All
• Compiler: All
• Release or debug mode: Both
• Specific flags used (if any):
• CGAL version: Latest (6.1)
• Boost version: irrelevant
• Other libraries versions if used (Eigen, TBB, etc.): for CGAL_Qt6, naturally Qt6 is required.