[PATCH 0/19] MR6766: dlls/wintypes: Implement Windows.Foundation.Collections.PropertySet.

[Vibhav Pant (＠vibhavp)]

The implementation is backed by a smaller `IWinePropertySetImpl` interface for core operations (insertion, lookup, removal, iteration), which currently uses an `rb_tree` to store `HSTRING`-`IInspectable *` value pairs.

If needed, this could be later swapped out with a hash table for performance reasons, as `PropertySet` does not have an enumeration order guarantee, at least according to the MSDN docs.