Consider extending `.Interface` pattern to things other than COM interfaces

[rickbrew]

For example,

public struct OSVERSIONINFOW : OSVERSIONINFOW.Interface
{
    public interface Interface { ... }
    ...
}

public struct OSVERSIONINFOEXW : OSVERSIONINFOEXW.Interface
{
    public interface Interface : OSVERSIONINFOW.Interface { ... }
    ...
}

This would reify the inheritance relationships, and enable certain uses of generics and would be source-generator friendly (like, I can generate my own __cast() "operator" methods).

Fields, which would have to be exposed as ref properties, might be best left out of the interfaces. Otherwise it would greatly increase friction for implementing and using them (hard to take the address of things).

[rickbrew]

This might also be useful for the 32 / 64 structs, but it would require some further noodling

[DllImport("shell32", ExactSpelling = true)]
public unsafe static extern BOOL ShellExecuteExW(void* pExecInfo);

public unsafe static extern BOOL ShellExecuteExW<TSHELLEXECUTEINFOW>(TSHELLEXECUTEINFOW* pExecInfo)
    where TSHELLEXECUTEINFOW : unmanaged, SHELLEXECUTEINFOW.Interface
{
    return ShellExecuteExW((void*)pExecInfo);
}

public struct SHELLEXECUTEINFOW : SHELLEXECUTEINFOW.Interface
{
    public interface Interface { }
}

public struct SHELLEXECUTEINFO32W : SHELLEXECUTEINFO32W.Interface
{
    public interface Interface : SHELLEXECUTEINFOW.Interface { }
}

public struct SHELLEXECUTEINFO64W : SHELLEXECUTEINFO64W.Interface
{
    public interface Interface : SHELLEXECUTEINFOW.Interface ​{ }
}

[rickbrew]

This idea could potentially go as far as every struct having a .Interface, but I think it's more appropriate to keep it limited to structs which either already have inheritance (e.g. OSVERSIONINFOW and IUnknown), or have multiple forms (e.g. SHELLEXECUTEINFO{32,64}W)