ENT-3187 Check that we're not calling toList on concurrent collections (#4828)

* ENT-3165 Kotlin toList() does not work on concurrent collections.  OS backport.

ENT-3165 Added comment.

* ENT-3187 Additional use of toList() on concurrent data structure.

core/src/main/kotlin/net/corda/core/internal/LazyPool.kt

@@ -62,7 +62,8 @@ class LazyPool<A>(
      */
     fun close(): Iterable<A> {
         lifeCycle.justTransition(State.FINISHED)
-        val elements = poolQueue.toList()
+        // Does not use kotlin toList() as it currently is not safe to use on concurrent data structures.
+        val elements = ArrayList(poolQueue)
         poolQueue.clear()
         return elements
     }