[pigeon] Add local-only Kotlin integration tests

[stuartmorgan-g]

Adds a new test target to run the new shared integration tests on Kotlin, and adds the necessary native-side plumbing.

This is not run by default because it requires a device or emulator to be present, and we don't have that set up for CI yet (and we don't yet have a different script entrypoint for manual vs CI tests).

Enabling this in CI is tracked in
flutter/flutter#111505, but landing it now allows for better manual testing of generator changes during development.

Part of flutter/flutter#111505

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• 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.)
• 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 listed 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 this PR is exempt from version changes.
• 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.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

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.

[stuartmorgan-g]

This code is duplicated from the repo tooling (with minor changes). While it's not ideal to duplicate it, it's not much code, and restructuring everything to allow using the repo tooling directly on Pigeon's tests (and thus eliminating most of run_tests.*) is a much bigger project that I don't want to gate other work.

[tarrinneal]

repo_checks test is mad about the copied tooling file. Is there an override for that check? Or should it just be added to a '3rd party' folder as suggested?

[stuartmorgan-g]

I just forgot to add the license/copyright boilerplate. It's not third-party code, since we wrote the original copy.