Repository: opencv
Issue: OpenCVDetectPython.cmake cannot find correct python libs in venv
Labels: feature,category: build/install

<!--
If you have a question rather than reporting a bug please go to https://forum.opencv.org where you get much faster responses.
If you need further assistance please read [How To Contribute](https://github.com/opencv/opencv/wiki/How_to_contribute).

This is a template helping you to create an issue which can be processed as quickly as possible. This is the bug reporting section for the OpenCV library.
-->

##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
-->

- OpenCV => 4.5.3
- Operating System / Platform => any major linux distro: CentOS8, fedora34, ubuntu20.04 ...
- Compiler => clang10

##### Detailed description

<!-- your description -->

After activate the venv and run cmake config:
```
Found PythonInterp: /opt/venv-74a3d1fd0900899b80dfa870337f6bb2/bin/python (found suitable version "3.9.5", minimum required is "2.7")
...
Could NOT find PythonLibs (missing: PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS)
```
This problem is caused by the deprecated `FindPythonLibs`, it is too old and has many unfixed bugs. Please use `FindPython` which actually use `python -c "from distutils.sysconfig import get_python_inc; print(get_python_inc())"` to find the include dir and 
`python -c "import distutils.sysconfig as sysconfig; print(sysconfig.get_config_var('LIBDIR'))"` to find the libs.

from cmake document:
```
Deprecated since version 3.12: Use FindPython3, FindPython2 or FindPython instead.
```

since in the `OpenCVDetectPython.cmake` it already conditioned with cmake version 3.12+, I think we should use FindPython there when cmake version >= 3.12 for much better python support

##### Steps to reproduce

<!-- to add code example fence it with triple backticks and optional file extension
    ```.cpp
    // C++ code example
    ```
 or attach as .txt or .zip file
-->

##### Issue submission checklist

 - [x] I report the issue, it's not a question
   <!--
   OpenCV team works with forum.opencv.org, Stack Overflow and other communities
   to discuss problems. Tickets with question without real issue statement will be
   closed.
   -->
 - [x] I checked the problem with documentation, FAQ, open issues,
       forum.opencv.org, Stack Overflow, etc and have not found solution
   <!--
   Places to check:
   * OpenCV documentation: https://docs.opencv.org
   * FAQ page: https://github.com/opencv/opencv/wiki/FAQ
   * OpenCV forum: https://forum.opencv.org
   * OpenCV issue tracker: https://github.com/opencv/opencv/issues?q=is%3Aissue
   * Stack Overflow branch: https://stackoverflow.com/questions/tagged/opencv
   -->
 - [x] I updated to latest OpenCV version and the issue is still there
   <!--
   master branch for OpenCV 4.x and 3.4 branch for OpenCV 3.x releases.
   OpenCV team supports only latest release for each branch.
   The ticket is closed, if the problem is not reproduced with modern version.
   -->
 - [ ] There is reproducer code and related data files: videos, images, onnx, etc
   <!--
   The best reproducer -- test case for OpenCV that we can add to the library.
   Recommendations for media files and binary files:
   * Try to reproduce the issue with images and videos in opencv_extra repository
     to reduce attachment size
   * Use PNG for images, if you report some CV related bug, but not image reader
     issue
   * Attach the image as archive to the ticket, if you report some reader issue.
     Image hosting services compress images and it breaks the repro code.
   * Provide ONNX file for some public model or ONNX file with with random weights,
     if you report ONNX parsing or handling issue. Architecture details diagram
     from netron tool can be very useful too. See https://lutzroeder.github.io/netron/
   -->