Kotlin multiplatform

[marcguilera]

Is your feature request related to a problem? Please describe.
It would be cool to get Kotlin Multiplatform support for pants in addition to the current JVM one. The tech is still somewhat new but it's already being used by a number of known names. This is currently not supported by bazel or buck so it may also be a good chance to get ahead in language support.

Describe the solution you'd like

• Dependencies: Dependencies are distributed through maven, so the plumbing for JVM may be reusable. Additionally the dependency inference logic can also be used from the existing Kotlin support.
• There would need to be a way to define sourceSet variations (ie: JVM, JS, Common, etc).
• I would start with basic build support but down the line it would be powerful to be able to build actual applications.

Describe alternatives you've considered

• Currently there is only good support for this using the Gradle plugin but that can still be used as an inspiration.

Additional context

• This may or may not depend on efforts to bring javascript to pants.
• As stated above, to build actual applications there would need to be support for iOS, Android, etc which probably would be specific rules that may consume the binaries produced by the kotlin rules.
• A question to build kotlin multiplatform from the CLI to be used in Bazel is here.