Simplify parameter bindings

[kennykerr]

This update builds on #2343 and dramatically simplifies input parameter bindings, somethings that's always been rather complicated as we've attempted to model convertibility in Rust. Rather than depend on thousands of From and TryFrom implementations, types now implement the marker traits called CanInto and CanTryInto that do nothing but indicate to the windows crate that such types are convertible. The various Windows APIs can then rely on these traits to transform input arguments in the most efficient way possible, either casting directly to a parent interface (in a COM hierarchy) or calling QueryInterface when a conversion is expected (in a WinRT hierarchy).

The end result is a simpler abstraction with far less code. Specifically, it avoids generating around 7,000 From and TryFrom implementations. That amounts to a lot of functions that the Rust compiler doesn't have to parse, saving on build time.

[kennykerr]

Forgot to merge - here's the new PR: #2360