Subclass WinUI Window to hook native win32 events

[Redth]

To do some things in WinUI we need to use win32 API's still.

This adds support to subclass the Window and start listening for windows native messages, and exposes them as a lifecycle event for other things to use.

For instance you could now use this:

public void Configure(IAppHostBuilder appBuilder)
{
	appBuilder
		.UseMauiApp<App>()
		.ConfigureLifecycleEvents(lifecycle => {
#if WINDOWS
			lifecycle
				.AddWindows(windows => windows.OnNativeMessage((window, args) => {
					if (args.MessageId == WindowsNativeMessageIds.WM_DPICHANGED) {
						// The DPI has changed on the system
					}
				}));
#endif
	});
}

[mattleibow]

How do we want to do this? Just these? All? This casing? Pascal case?

Maybe for now we can keep this internal?

[Redth]

Yeah we could just keep it internal for our own uses and maybe doc a url to a good way to find the id's.

I was torn between trying to provide some consts here for common events users may want, and exposing more individual events that propagate from these and get exposed in a more strongly named/typed way (like adding an OnThemeChanged to the lifecycle)

[jsuarezruiz]

Or maybe an enum like https://github.com/CommunityToolkit/Microsoft.Toolkit.Win32/blob/b9340a647db5cf011ac4056ee9805d56e8b91cd7/Microsoft.Toolkit.Win32.UI.Controls/Interop/Win32/WM.cs?

[dotMorten]

It might be worth rewriting these lines to :

_NativeMessage?.Invoke(this, new WindowsNativeMessageEventArgs(hWnd, msg, wParam, lParam));

That way you don't allocate the event arguments unless there's a listener.