xfeatures2d / python: no create() function for MSDDetector

[berak]

System information (version)

• OpenCV => 3.4.x, 4.x
• Operating System / Platform => Windows 64 Bit (any)
• Compiler => python3

Detailed description

there is no cv2.xfeatures2d.MSDDetector_create() function available, because there's a CV_WRAP missing here: https://github.com/opencv/opencv_contrib/blob/0da725559ea38418acce55c9a7cabe9fe72921ee/modules/xfeatures2d/include/opencv2/xfeatures2d.hpp#L285

(and a simple cv2.xfeatures2d.MSDDetector() will segfault, once we try to call any method on it)

Steps to reproduce

help(cv2.xfeatures2d.MSDDetector)

Issue submission checklist

• [x] I report the issue, it's not a question
• [x] I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• [x] I updated to the latest OpenCV version and the issue is still there
• [x] There is reproducer code and related data files: videos, images, onnx, etc