packages [pigeon] Kotlin implementation for ProxyApis

Kotlin portion of https://github.com/flutter/flutter/issues/134777

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 linked to 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.
[x] I updated/added relevant documentation (doc comments with ///).
[x] I added new tests to check the change I am making, or this PR is test-exempt.
[x] All existing and new tests are passing.

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Mar 21 '24 19:03 bparrishMines

Are you planning to add the full implementation and test suite to this pr?

Apr 10 '24 20:04 tarrinneal

Are you planning to add the full implementation and test suite to this pr?

I wasn't planning on doing that for this PR, but I can if you prefer the full implementation. This PR just adds the Kotlin ProxyApi utility classes, including the InstanceManager and the tests for it. And also the bare minimum ProxyApi class declaration.

Apr 11 '24 16:04 bparrishMines

@tarrinneal I updated the PR to have the full implementation and tests. Its ready for a review.

Apr 17 '24 19:04 bparrishMines

From android triage: Reid is out for the rest of this week, does this need another Android reviewer in the meantime, or is work still ongoing?

Aug 22 '24 18:08 gmackall

@bparrishMines I think there needs to be some plumbing added to have the kotlin files generate using the tool/generate script

Aug 27 '24 17:08 tarrinneal

@tarrinneal What do you mean? I have been using dart run tool/generate.dart to generate the Kotlin code successfully. Is this the script you are referring to?

Aug 27 '24 18:08 bparrishMines

@tarrinneal What do you mean? I have been using dart run tool/generate.dart to generate the Kotlin code successfully. Is this the script you are referring to?

yep, If it's working then don't worry about it :)

Aug 27 '24 19:08 tarrinneal