Show blue contraflow arrow for oneway:bicycle=no on one-way ways

[tordans]

Problem

On one-way streets that allow contraflow cycling (oneway=yes + oneway:bicycle=no, or oneway=-1 with the same bicycle tag), Go Map!! today shows only a single black chevron for the general (motor) direction. Mappers cannot see at a glance that cyclists may legally travel the opposite way without opening the POI editor.

This is a common tagging pattern on urban cycle infrastructure (one-way street with contraflow cycling). We want the map to communicate “cars this way, bikes both ways” directly on the canvas.

Implementation notes (Cursor)

• OSM key: oneway:bicycle (documented in code above allowsBicycleContraflow()).
• Added OsmWay.allowsBicycleContraflow() — returns true when isOneWay != .NONE and tags["oneway:bicycle"] == "no". Does not change computeIsOneWay() / turn-restriction logic.
• Refactored one-way chevron drawing in EditorMapLayer into makeOneWayArrowLayer(at:direction:chevronLength:alongWayOffset:fillColor:zPosition:).
• Black arrow: motor/general direction at the sampled point on the way.
• Blue arrow: opposite direction, shifted along the way behind the black tip (< then > on the same centerline; longitudinal offset 3× chevron length so the pair does not overlap). Black is drawn on top of blue.
• Placed along the way with the same invoke(alongScreenClippedWay:offset:interval:) spacing as today (offset 50, interval 100).

Out of scope (follow-up): other mode-specific exceptions (oneway:foot, oneway:bus, …).

Testing notes (@tordans)

1. Find or create a way with oneway=yes and oneway:bicycle=no like https://www.openstreetmap.org/way/25509293 — expect tandem < (blue) > (black) on the same line along the way (not offset above/below the road).
2. Same tags with oneway=-1 — black points backward; blue forward, still inline behind black along the way. – did not test, assumed correct
3. oneway=yes without oneway:bicycle=no — only the black chevron (no regression).
4. oneway:bicycle=no on a non-one-way way — no arrows (unless highlighted by selection) – did not test, assumed correct
5. Zoom in/out and pan — chevrons stay aligned on the way centerline and remain readable.

Before	After
bicycle-oneway--after.min.mov	bicycle-oneway--after.min.mov