Add an option to set the ROI of an algorithm to an annotation

[manthey]

Also, create an annotation from an ROI.

This would work by default only with rectangles and polygons. A more sophisticated process would set the ROI from image annotations based on their size or mask, convert ellipses to polygons, etc.

[manthey]

We could do this as an entry in the annotation element context menu. IF there is a region option in a CLI panel, then the element context menu could have a "Set ROI". Ideally, this would use the most complex allowed ROI based on the selection (e.g, handle multiple polygons, rectangles, points if allowed).

The inverse is a bit trickier, since there would need to be a way to pick from the region menu to add element(s) to the current annotation, which would require knowing if there was a current annotation. That could be a different issue and PR.