[google_maps_flutter_web] Initial support for custom overlays

[elitree]

This is a resubmission of https://github.com/flutter/plugins/pull/6982 from the now archived flutter plugins repo. I'm submitting the changes from the original author, @AsturaPhoenix. The original description is below.

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Saves tile bytes to blobs and uses img elements to decode and render. Does not implement opacity, perform caching, or serve placeholder images.

Issue: https://github.com/flutter/flutter/issues/98596

Known issues:

• https://github.com/flutter/flutter/issues/116132
• https://github.com/AsturaPhoenix/trip_planner_aquamarine/issues/22

Opening in draft to go through the checklist.

Pre-launch Checklist

• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x] I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• [x] I signed the CLA.
• [x] The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• [x] I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• [ ] I updated/added relevant documentation (doc comments with ///).
• [ ] I added new tests to check the change I am making, or this PR is test-exempt.
• [ ] All existing and new tests are passing.

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