Implement getHarrisKeypoints

[opatiny]

We already have a function to compute the Harris score (response) of a given point in an image, but we want to implement the function returning all the Harris keypoints for a given image. This feature was requested in image-js/image-js#628.

const keypoints = getHarrisKeypoints(image, options);

Wikipedia article for Harris corner detector: https://en.wikipedia.org/wiki/Harris_corner_detector

[TaihuLight]

@opatiny #image-js/image-js#628
Has this function been implemented in image-js-typescript?