Explore easing interop instance limitations

[elringus]

1. Consider marshaling only types with value semantics (structs, records and strings) and read-only collection interfaces (IReadOnlyCollection, IReadOnlyList). Other types (both concrete classes and interfaces) would be subject to instance bindings. Common collection types (array, list, dictionary) and their (mutable) interfaces (ICollection, IList, IDictionary) would have instance bindings as well, but with pre-built implementations on both sides (for example, to proxy APIs of JS array to C#'s List<> and vice-versa). Currently, only interfaces outside of system namespace are subject for instance bindings.
2. Allow interop instances inside other interop instances. Currently, only top-level args (inside static export/import methods) are subject for instance bindings.