Describe the feature and motivation

In PR !21942 new functionality was added but without an issue that describes what the new functionality does and why it was needed/desired. Additionally the public API was extended by an undocumented method.

The main change is somewhat clear: SimpleBlobDetector was introduced as a feature2d class that detects key points in a image. Thus only the center points of the detected contours are returned which is much less useful than the full contour for further processing. Since the method findBlobs is protected, a new public method was introduced to get the blobs of the last detect call as long as the param collectBlobs was set to true.

Overall a good change to make the SimpleBlobDetector usable but it lacks documentation. Without looking at the code it's completely unclear what the things do. Neither the documentation nor the sample code was updated.

I would be happy to provide a few lines of explanation for the next reader now that I have stumbled upon this and read the source code.

Additional context

No response