Call compactIfPossible where it's possible in BinaryJava*

It helps to avoid retaining a lot of redundant empty SmartList's
instances

core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt

@@ -132,7 +132,7 @@ inline fun <T> measureTimeMillisWithResult(block: () -> T) : Pair<Long, T> {
     return Pair(System.currentTimeMillis() - start, result)
 }
 
-public fun <T> Iterable<Iterable<T>>.flattenTo(c: MutableList<T>): List<T> {
+fun <T, C : MutableCollection<in T>> Iterable<Iterable<T>>.flattenTo(c: C): C {
     for (element in this) {
         c.addAll(element)
     }