Fixed Python signatures in Doxygen documentation.

[asmorkalov]

Fixes #23133

Python bindings signatures are added to Doxygen documentation with pyopencv_signatures.json. The file is generated by python bindings generator. The constructors are there, but namespace is handled incorrectly, e.g.:

    "cv::aruco::Dictionary::cv::aruco::Dictionary::Dictionary": [
        {
            "name": "cv.aruco.Dictionary",
            "arg": "",
            "ret": "<aruco_Dictionary object>"
        },
        {
            "name": "cv.aruco.Dictionary",
            "arg": "bytesList, _markerSize[, maxcorr]",
            "ret": "<aruco_Dictionary object>"
        }
    ],

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[asmorkalov]

@mshabunin could you take a look too.