[google_maps_flutter_web] Add editable polyline and polygon support

[lume-code]

⚠️ Draft — blocked on the platform interface landing.
This is part 2 of 3 splitting #11492 along the federated plugin, per the
contributing guidelines.
It depends on google_maps_flutter_platform_interface 2.16.0 (#11492). Once that lands in main, CI's pathified jobs (make-deps-path-based) resolve the in-repo interface automatically; this PR will be marked ready then (and is fully green once 2.16.0 publishes to pub.dev).

Implements editable polylines and polygons on the web platform, using the native Google Maps JavaScript API editable feature.

Changes — google_maps_flutter_web (0.6.2+3 → 0.7.0)

• Wires editable through _polylineOptionsFromPolyline() / _polygonOptionsFromPolygon().
• Subscribes to the path MVCArray events (onSetAt, onInsertAt, onRemoveAt) in PolylineController / PolygonController.
• Emits PolylineEditEvent / PolygonEditEvent (including polygon holes) over the shared event stream.
• Recreates the controller on change so edit listeners are rewired when editable toggles.
• Adds integration tests for the edit events in example/latest/integration_test/.

This feature is web-only; the editable property is silently ignored on Android and iOS.

Part of #11492 · Interface PR: #11492 · App-facing PR: #11920 · 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 (Blocked: depends on the unpublished interface 2.16.0 from [google_maps_flutter_platform_interface] Add editable polyline and polygon API #11492. Verified locally against the in-repo interface.)

Footnotes

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