[webview_flutter_platform_interface] Add support for getting cookie

[khaled-0]

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

#10833

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• 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 under¹.
• 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 under¹.
• I updated/added any relevant documentation (doc comments with ///).
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[flutter-dashboard]

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[gemini-code-assist]

Code Review

This pull request introduces support for retrieving cookies by adding a getCookies method to the PlatformWebViewCookieManager interface. The changes are well-contained within the platform interface package, including necessary updates to pubspec.yaml and CHANGELOG.md. My review focuses on improving documentation clarity and ensuring test coverage for the new functionality, in line with repository guidelines.

[gemini-code-assist]

The repository's contribution guide requires that code changes are tested. Please add a unit test for the new getCookies method to verify that its default implementation throws an UnimplementedError.

References

1. The style guide states that code should be tested. ^(link)

[gemini-code-assist]

There's a minor typo in the documentation. It should be 'cookies' (plural) to be consistent with the method returning a list.

Suggested change

	/// Gets a list of existing cookie for specified domain from all
	/// Gets a list of existing cookies for specified domain from all