Dependency File Rule Keys don't work for Kotlin

Created by: IanChilds

Right now Dependency File Rule Keys (https://buck.build/concept/rule_keys.html#manifest_based_rule_keys) are turned off for Kotlin.

For Java, we implement this by passing an implementation of FileManagerListener, ClassUsageTracker to the FileManager that we pass into the CompilationStep (see Jsr199JavacInvocation).

In Kotlin, it doesn't look like we pass a FileManager to the compiler. Does anyone know how we could get hold of which files we actually accessed by the compiler?

cc @jkeljo, @kageiit, @tyvsmith, @thalescm in case anyone has ideas