[google_maps_flutter] Add editable polyline and polygon support (web)

[lume-code]

⚠️ Draft — blocked on the platform interface (and web) landing.
This is part 3 of 3 splitting #11492 along the federated plugin, per the
contributing guidelines.
It depends on google_maps_flutter_platform_interface 2.16.0 (#11492) and google_maps_flutter_web 0.7.0 (#11919). Once those land in main, CI's pathified jobs (make-deps-path-based) resolve the in-repo packages automatically; this PR will be marked ready then (and is fully green once both publish to pub.dev).

Wires the app-facing package up to the editable polyline/polygon edit events.

Changes — google_maps_flutter (2.17.1 → 2.18.0)

• Subscribes to the platform interface onPolylineEdited / onPolygonEdited streams in controller.dart.
• Dispatches them to the onEdited callbacks on Polyline / Polygon in google_map.dart.
• Adds tests for the dispatch and for editable change propagation.

Usage

Polyline(
  polylineId: const PolylineId('editable-route'),
  points: [...],
  editable: true,
  onEdited: (List<LatLng> updatedPoints) {
    // Handle the updated path.
  },
)

Editing is currently web-only; the editable property is silently ignored on Android and iOS.

Part of #11492 · Interface PR: #11492 · Web PR: #11919 · Fixes flutter/flutter#71248

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing. (Blocked: depends on the unpublished interface 2.16.0 ([google_maps_flutter_platform_interface] Add editable polyline and polygon API #11492) and web 0.7.0 ([google_maps_flutter_web] Add editable polyline and polygon support #11919). Verified locally — all 120 package tests pass against the in-repo dependencies.)

Footnotes

1. See the test exemption and version/CHANGELOG exemption docs for details. ↩ ↩²