[google_maps_flutter_web] Fix AdvancedMarker anchors on web

[3ph]

Fixes AdvancedMarker anchor handling in google_maps_flutter_web.

Previously AdvancedMarker.anchor was not applied on web, so custom advanced marker content was positioned as if it used the default anchor. This caused markers with non-default anchors to appear offset from their intended map coordinates.

This PR converts Flutter marker anchor offsets into the Google Maps JavaScript Advanced Marker anchorLeft and anchorTop CSS offset properties when creating marker options, and reapplies those properties when an existing advanced marker is updated.

Adds integration test coverage for creating and updating an AdvancedMarker with custom anchors.

Addresses flutter/flutter#80578.

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• I linked to at least one issue that this PR fixes in the description above.
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• I updated/added any relevant documentation (doc comments with ///).
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[gemini-code-assist]

Code Review

This pull request implements AdvancedMarker anchor handling for the Google Maps Flutter Web plugin. It introduces helper functions to convert anchor offsets to CSS percentage strings and apply them as anchorLeft and anchorTop properties on the underlying AdvancedMarkerElement and its options. Additionally, an integration test has been added to verify that anchors are correctly set and updated. I have no feedback to provide.

[gemini-code-assist]

Code Review

This pull request fixes the anchor handling for AdvancedMarker on the web platform by introducing helper functions to convert anchor offsets to CSS percentages and apply them to AdvancedMarkerElementOptions and AdvancedMarkerElement. It also adds an integration test to verify anchor positioning and updates, and bumps the package version to 0.6.2+4. There are no review comments, and I have no feedback to provide.

[stuartmorgan-g]

Thanks for the contribution! There are two email addresses associated with the commits in this PR, and only one has a CLA on file. You'll need to either sign the CLA for the second address, or if using it was unintentional, amend your commits and re-push. Once that's done, please mark as Read for Review.

[gemini-code-assist]

Code Review

This pull request implements AdvancedMarker anchor handling on the web platform by converting anchor offsets to CSS percentage strings and applying them to the marker options, supported by new integration tests. Feedback suggests addressing potential floating-point precision issues in the percentage calculation to prevent verbose CSS output.

[gemini-code-assist]

Floating-point multiplication (e.g., -anchor * 100) can sometimes introduce precision artifacts (for example, -0.14 * 100 results in -14.000000000000002 in Dart/JS). This can cause the strict equality check percentage == percentage.roundToDouble() to fail, leading to unnecessarily verbose CSS percentage strings like '-14.000000000000002%' instead of '-14%'.

Using a small epsilon check when comparing the percentage to its rounded integer value will make the output cleaner and more robust against floating-point precision issues.

Suggested change

	String _advancedMarkerAnchorToCssOffset(double anchor) {
	final double percentage = -anchor * 100;
	if (percentage == percentage.roundToDouble()) {
	return '${percentage.toInt()}%';
	}
	return '$percentage%';
	}
	String _advancedMarkerAnchorToCssOffset(double anchor) {
	final double percentage = -anchor * 100;
	final int rounded = percentage.round();
	if ((percentage - rounded).abs() < 1e-9) {
	return '$rounded%';
	}
	return '$percentage%';
	}

[stuartmorgan-g]

Why is this using unsafe dynamic lookup? If there are properties that aren't reflected in google_maps, they should be added upstream, rather than bypassing the wrapper.