[google_maps_flutter] Fix various Java warnings

[stuartmorgan-g]

Fixes various warnings and suggestions that show up in Android Studio:

• Adopt pattern and switch expressions now that we require Java 17
• Add some missing nullability annotations
• Removes some dead code left over from before the Pigeon migration
• Fixes typos

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.

[stuartmorgan-g]

test-exempt: code refactor with no semantic change

[stuartmorgan-g]

There are still a lot of warnings about potential NPEs (mostly, but not all, in cases where we'd have to call native methods in the wrong order for them to happen), but I didn't try to address those here since those would be much more involved fixes. These are almost all just auto-apply of IDE fixes.

[gemini-code-assist]

Code Review

This pull request updates the Android Google Maps implementation to resolve Java warnings and modernize the code. Significant changes include the adoption of Java 17 features such as pattern matching for instanceof and switch expressions, the use of try-with-resources for InputStream handling, and the addition of nullability annotations across multiple classes. The PR also removes unused imports, methods, and the ProxyLifecycleProvider class, while fixing minor typos in parameter names. Review feedback highlights opportunities to improve consistency by placing nullability annotations before access modifiers and ensuring all relevant fields are annotated.

[stuartmorgan-g]

Oops, I had commits that were supposed to be a follow-up PR that I apparently landed in this branch. I'll fix and force-push shortly.