Binder: a public companion object is reachable from Python as a value (Owner.Companion) #322

Context: Card(modifier=Modifier) still fails in real Compose (pythonx-compose SPEC S6.2 partial). Kotlin's empty Modifier is the companion object Modifier.Companion itself, and the binder never binds a companion instance (only its members: Owner.prop is called as Owner.Companion.prop). So pythonx-compose has nothing to hand to register_empty (#308).
Generic feature, no Compose name in the binder: a Kotlin-public companion object of a public class becomes a value from Python, reached by its Kotlin name (Owner.Companion, or the companion's own name if it has one). The generated Kotlin source names the companion and kotlinc compiles it to GETSTATIC Owner.Companion (no JVM name lookup, rule 12.4).
Completion: SPEC item; walker and runtime tests; Modifier.Companion from Python is a Modifier and works as an argument (e.g. register_empty(Modifier, lambda: Modifier.Companion) then Card(modifier=Modifier) renders), red before. Design is reported to the coordinator before implementation (adds public Python meaning).