Used for snapping geometries within a set of features to other
features from that same set.
Just like QgsGeometrySnapper, except that where QgsGeometrySnapper
requires a separate reference layer to snap to
QgsInternalGeometrySnapper snaps *within* a single layer. E.g.
allows you to close gaps within that layer.
With a new option to prefer to snap to closest point on geometry.
The old behaviour was to prefer to snap to nodes, even if a node
was further from the input geometry than a segment. The new option
allows you to snap geometries to the closest point, regardless
of whether it's a node or segment.
