Investigate Java collection wrappers performance

Investigate if any of the methods provided by our Java collection wrappers (`JavaList`, `JavaDictionary`, etc.) could be implemented more efficiently.

For example, [`JavaList`](https://github.com/xamarin/xamarin-android/blob/main/src/Mono.Android/Android.Runtime/JavaList.cs) implements `ToArray ()` by calling `java.util.List.get (int)` for each item in the `List`, resulting in a lot of marshalling overhead.

Could we instead call [`java.util.List.toArray ()`](https://developer.android.com/reference/java/util/List?hl=en#toArray()) to retrieve all of the items in one call?

Another possibility might be to add something like `ToImmutableList ()` to efficiently move a copy of the list to C# that no longer needs to be kept in sync with Java?