README: add kotlin implementation

[jbordeau]

No description provided.

[panmari]

Thanks for your submission! I'm afraid implementations not affiliated with Google are out of scope.

[jmr]

I don't see any reason we can't link this. re2 links all kinds of implementations.

https://github.com/google/re2/blob/c84a140c93352cdabbfb547c531be34515b12228/README#L38

[alan-strohm]

Also, the Kotlin version is already mentioned in https://github.com/google/s2geometry/blob/master/README.md

[flwyd]

It doesn't look like the Kotlin project has been updated since its initial implementation in 2021. @jbordeau could you say more about the development plans of the Kotlin library?

I also don't see anything on that project's README indicating why someone should use the Kotlin version over https://github.com/google/s2-geometry-library-java which is maintained by the same team which maintains the C++ S2 library. The Java project was fairly stale until early 2021, but is now closer to feature parity with C++, with a goal of keeping the two projects aligned in terms of APIs, precision, and performance.

Jesse, it looks like you approved the PR to add the Kotlin link to the C++ README. Since there's already an officially-maintained JVM implementation, I would recommend that the S2 libraries not link to a separate Kotlin version, since it's not interoperable with the Java classes. Linking to both would, I think, invite user confusion.
I think the RE2 links aren't an even comparison: those all look like language-idiomatic wrappers around the C++ re2 implementation, rather than a fork reimplemented in a different language.

[jmr]

It doesn't look like the Kotlin project has been updated since its initial implementation in 2021

If it's dead, then let's not link to it. Pointing people to it will probably end in unsupported frustration.

I also don't see anything on that project's README indicating why someone should use the Kotlin version over https://github.com/google/s2-geometry-library-java

Kotlin is more complete.

Jesse, it looks like you approved the PR to add the Kotlin link to the C++ README.

I'll remove it unless we hear about its liveness.

[jmr]

Reopen this if the kotlin implementation is still maintained.