python3Packages.opencv should also export the wrapper packages

[pasqui23]

Describe the bug

python3Packages.opencv only exports the opencv package.
However many python packages depend on the prebuilt opencv-python(https://pypi.org/project/opencv-python/) or opencv-python-headless(https://pypi.org/project/opencv-python-headless/) pip package, as they are a drop in replacement for each other.
Also if opencv is built with the contrib extensions opencv-contrib-python(https://pypi.org/project/opencv-contrib-python/) should be exposed too.

Steps To Reproduce

Steps to reproduce the behavior:

1. Try to package a python package depending on opencv-python like medialib
2. Add opencv to propagatedBuildInputs
3. Build it

Expected behavior

Build succeeds without problems

Additional context

I've encountered this while trying to build #153255
The suggested workaround of patching the dependant packages by removing the opencv-python dependency would not work if we source the package from a wheel for example.

It also duplicate works that should be done only in one place

Notify maintainers

@jonringer @mdaiter @basvandijk

Metadata

• system: "x86_64-linux"
• host os: Linux 5.16.2, NixOS, 22.05 (Quokka)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.5.1
• nixpkgs: /nix/store/8jc465d8r1mrjxb7j6wx7qc7d95frv0k-source

[jonringer]

It would probably be easiest to have just a stub setup.py, and just have a meta package which exports the 4 packages built by https://github.com/opencv/opencv-python

[jonringer]

related: #153373 (comment)

[pasqui23]

It would probably be easiest to have just a stub setup.py, and just have a meta package which exports the 4 packages built by https://github.com/opencv/opencv-python

opencv-contrib-python should be produced only if opencv is built with the contrib extensions.

I guess this would be easier if it is all evaluated from inside opencv package