Provide helpers to bridge Windows.Foundation.Collections and Swift collections

It turns out supporting a conversion from Swift.Array<Element> to IVector<Element> in the support module might not be feasible. Trying to summarize:

IVector<T> virtual tables rely on T-specific code generation because the ABI for things like the IndexOf(T) function pointer is incompatible between a struct and a reference type, for example. C++ can generalize this because of its templates, but Swift cannot.
The object generated needs to have a QueryInterface implementation that knows about both IVector and IIterable as to be able to synthesize both virtual tables.

Maybe this is implementable with a class ArrayVector<IVectorProjection, IIterableProjection>: WinRTExport<IInspectableProjection>

tristanlabelle / swift-winrt

Provide helpers to bridge Windows.Foundation.Collections and Swift collections #26