[google_maps_flutter] Add color scheme support to web implementation

[stuartmorgan-g]

Web portion of #10471, incorporating review feedback and some other minor cleanup.

Part of flutter/flutter#176445

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Footnotes

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[gemini-code-assist]

Code Review

This pull request adds colorScheme support to the web implementation. It updates pubspec.yaml and CHANGELOG.md, and modifies convert.dart to apply the colorScheme to the map options. A review comment has been added suggesting to only apply the colorScheme when a mapId is provided, as the feature is for cloud-based maps.

[gemini-code-assist]

The colorScheme property should only be applied when a mapId is present, as this feature is for cloud-based maps on the web. Please wrap this logic in a check for configuration.mapId.

Suggested change

	final gmaps.ColorScheme? jsColorScheme = _gmapTypeColorSchemeForPluginColor(
	configuration.colorScheme,
	);
	if (jsColorScheme != null) {
	options.colorScheme = jsColorScheme;
	}
	if (configuration.mapId != null) {
	final gmaps.ColorScheme? jsColorScheme = _gmapTypeColorSchemeForPluginColor(
	configuration.colorScheme,
	);
	if (jsColorScheme != null) {
	options.colorScheme = jsColorScheme;
	}
	}

[stuartmorgan-g]

I don't see anything in the docs that actually requires a mapId.

[auto-submit]

autosubmit label was removed for flutter/packages/11279, because - The status or check suite Windows_x64 repo_tools_tests has failed. Please fix the issues identified (or deflake) before re-applying this label.