The annotations component has no UI PMA.UI.Components.Annotations, but provides the methods to interact with
a PMA.UI.View.Viewport.
You can edit/update a MultiPoint annotation in this tutorial by passing an existing feature in PMA.UI.Components.Annotations#startDrawing.
You can get the number of points of an existing MultiPoint annotation using PMA.UI.Components.Annotations#getSelection[0].metaData.PointCount
as seen in this tutorial