Add experimental coroutines compiler flag

[samhill303]

If we add the compiler flag for experimental coroutines we can remove the annotations everywhere we use it.

tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
        freeCompilerArgs += ["-Xuse-experimental=kotlinx.coroutines.ExperimentalCoroutinesApi"]
    }
}