[stuartmorgan-g]

Converts google_sign_in_android implementation code from Java to Kotlin.

Similar to my other conversions, the process was:

• Use the Android Studio deterministic auto-conversion.
• Do a bunch of manual cleanup, as separate commits by topic.
• Do a local Gemini review for where the code could be improved as Kotlin code, and address most of that feedback.

This also removes the bridge code that allowed using Result from Java, now that it is no longer necessary.

Part of flutter/flutter#188630
Fixes flutter/flutter#193432

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• 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 followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under¹.
• 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 under¹.
• All existing and new tests are passing.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩²

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[gemini-code-assist]

Code Review

This pull request converts the Android implementation of the google_sign_in plugin from Java to Kotlin, removing the legacy Java files and updating the package version to 7.2.18. Feedback on the changes recommends executing getCredentialAsync and clearCredentialStateAsync callbacks on the main thread using ContextCompat.getMainExecutor(context) to ensure thread safety with Flutter's BinaryMessenger. Additionally, it is recommended to replace the double-bang operator (!!) with a safe-call operator (?.) on activityPluginBinding in disposeActivity() to prevent potential null pointer exceptions.