Proposal: Add virtual method for application exit in WINUI (C#)

Summary

Be able to hook on application exit just like the existing OnLaunched

Rationale

I'm using an existing code "C" code base using Interop (P/Invoke) calls from our existing system. I need to initialise the "library" on launch, but also need to "shutdown" that library properly when the application exits.
Right now, we're stuck to unload the library using the window close operation. But since we have multiple top level window, we need some weird code to make sure we perform the exit procedure on the "last window to close".

Would be nice to simply do that using an OnExit override on the Application class.

Note

Using WinUI in unpackaged C# application.