Fixes #1049. Partly.

cppwinrt separates the headers by namespace, and within each namespace into 'passes' where each pass has specific responsibilities. Structs for a given namespace all appear in the same header. There are limits to what C++ /WinRT can resolve in terms of struct dependencies across headers, but within a header, it sorts definitions so that structs consumed by other structs appear first. In the absence of dependencies, it follows metadata order, which is alphabetical.

There's an overlooked corner case in the dependency sorting. structs generally only contain plain data, with two exceptions: strings and nullable types (instances of IReference). The dependency checking code only looked at the exact type name when evaluating dependencies. If a struct contains an IReference<> to another struct, the dependency checking code would not detect the template parameter inside the IReference type.

Since this is a very constrained special case, I've chosen to code a fix that looks specifically for IReference. MidlRT and other tooling enforce this constraint. It could be generalized to parse template parameters out of the type name, but given there's only one exact type that can appear, this is complete and sufficient as written.