Chained Hulling Algorithm for Convex Hull Area of Canvas Alpha Threshold

This function calculates the convex hull of pixels in a given image's alpha channel (above a certain threshold - 64 by default) and returns the area of that hull.

This yields a decent approximation of the image content's area, in terms of space occupied by the image. This can then be used for, say, normalizing the size of icons on a menu, rather than trusting developers to figure out, which, in practice, doesn't really work.