[google_maps_flutter_web] Add Advanced markers support (web)

[aednlaxer]

This PR adds Advanced markers support to the web implementation of google_maps_flutter.
Approved combined PR: #7882
Approved and merged platform interface PR: #9737
Issue: #155526

Pre-Review Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• 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 updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy], or I have commented below to indicate which [version change exemption] this PR falls under[^1].
• I updated CHANGELOG.md to add a description of the change, [following repository CHANGELOG style], or I have commented below to indicate which [CHANGELOG exemption] this PR falls under[^1].
• 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 under[^1].
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This PR adds support for Advanced Markers to the web implementation of google_maps_flutter. The changes are extensive and well-structured, refactoring the marker handling logic to support both legacy and advanced markers through generics and abstract classes. New tests have been added for the new functionality, and existing ones have been updated. The implementation looks solid, but I've found a couple of critical issues that would prevent the code from compiling or running correctly.

[gemini-code-assist]

There's a typo here. clusterManagersController is used, but it should be _clusterManagersController. This will cause a compilation error as clusterManagersController is not defined in this scope.

          clusterManagersController: _clusterManagersController!
              as ClusterManagersController<gmaps.AdvancedMarkerElement>,

[gemini-code-assist]

The implementation of getMarkerId has a couple of issues for AdvancedMarkerElement:

1. gmaps.AdvancedMarkerElement is an HTMLElement and does not extend gmaps.MVCObject. The cast marker as gmaps.MVCObject will fail at runtime when the marker is an AdvancedMarkerElement.
2. The id of an AdvancedMarkerElement is a standard DOM attribute, not a property set via MVCObject.set. It should be accessed directly from the element.

Here's a corrected implementation.

MarkerId getMarkerId(Object? marker) {
  final JSObject object = marker! as JSObject;
  if (object.isA<gmaps.Marker>()) {
    final gmaps.MVCObject mapObject = marker as gmaps.MVCObject;
    return MarkerId((mapObject.get('markerId')! as JSString).toDart);
  } else if (object.isA<gmaps.AdvancedMarkerElement>()) {
    final gmaps.AdvancedMarkerElement element =
        marker as gmaps.AdvancedMarkerElement;
    return MarkerId(element.id);
  } else {
    throw ArgumentError(
      'Must be either a gmaps.Marker or a gmaps.AdvancedMarkerElement',
    );
  }
}