when snapping line layers
Because the default behavior of the snapper is to insert extra
vertices into the snapped geometry in order to make it 'follow'
the reference geometries exactly, this can result in unwanted
results for line layers where the resultant snapped layer
has overlapping line segments.
Since we can't always know what the desired result is that the
user wants (maybe they do want overlapping lines), instead
give them control over the result by exposing extra enum
options which never insert extra vertices.
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.
