search functions should return unpacked nodes and edges

[oxidase]

As a left-over from the MLD shortest path plugin implementation in two stub functions unpacked_edges array is ignored and later created from unpacked_nodes via facade.FindEdge.

To simplify interfaces and avoid unnecessary work the search functions should return unpacked nodes and edges.

EDIT: removed 5.8 milestone after inspecting the shortest path plugin code: "easy" but not desirable solution requires duplication of paths concatenation logic.