edit operation on an annotation item
This is used for the item to return a representative geometry
of what the item would look like if the operation were to be
applied. It's used to generate a rubber band showing a preview
of the modification during interactive editing operations on
an annotation item.
For now all nodes just directly represent vertices in the item,
but the intention here is that they can represent any form of handle
which can be used to manipulate an item (e.g. a bezier curve point,
some "smart shape" handle for resizing or rotating an item, etc)
work correctly with curved geometry types, and tweak some API naming
accordingly
There's no need to be restrictive and only require linear geometries
for these items!
