Clarify identifier types used in data facade

[mjjbell]

Issue

The data facade interface contains numerous methods for looking up data points by identifiers.
Many of the parameters use the NodeID or EdgeID types. However, these two identifier types are used in three different contexts:

1. Node-based graph edges and nodes
2. Edge-based graph edges and nodes
3. Packed geometries (IDs not used by any graph)

Consider the use of identifier parameters in these examples:

a. EdgeID = edge-based edge

osrm-backend/include/engine/datafacade/datafacade_base.hpp

Line 91 in ec36319

virtual TurnPenalty GetWeightPenaltyForEdgeID(const EdgeID id) const = 0;

b. EdgeID = packed geometry

osrm-backend/include/engine/datafacade/datafacade_base.hpp

Line 97 in ec36319

virtual WeightForwardRange GetUncompressedForwardWeights(const EdgeID id) const = 0;

c. NodeID = edge-based node

osrm-backend/include/engine/datafacade/datafacade_base.hpp

Line 219 in ec36319

virtual bool IsLeftHandDriving(const NodeID id) const = 0;

d. NodeID = node-based node

osrm-backend/include/engine/datafacade/datafacade_base.hpp

Line 215 in ec36319

virtual util::guidance::BearingClass GetBearingClass(const NodeID node) const = 0;

This mixing of contexts within the same interface makes it difficult to understand the relationships and dependencies between the OSRM datasets.

Change

For 1. and 2. we continue to use the NodeID and EdgeID types, but change the interface parameter names to identify them as
edge-based or node-based graph properties.

For 3. we define a new type definition, PackedGeometryID.

By only updating the facade code, I'm hoping this is the smallest change needed to improve code understanding.

We could create separate typedefs for edge-based and node-based identifiers and use them throughout the codebase, but this would be a huge change without the benefit of compile time checks.

A better next step would be to strongly type these definitions, leveraging the Alias template already used for OSM identifiers, but this also requires significant work.

Tasklist

• review
• adjust for comments
• cherry pick to release branch