strongFlatMapCollectionTo
inline fun <T, R, C : MutableCollection<in R>> Provider<Collection<T>>.strongFlatMapCollectionTo(crossinline makeCollection: (size: Int) -> C, crossinline transform: (T) -> Iterable<R>): Provider<C>
Creates and returns a new Provider that flat-maps the elements of the Collection obtained from this into a collection created by makeCollection using the transform function.
makeCollection and transform should be pure functions.