Report better errors when a library doesn't support AoT

### Describe the bug

This is a follow up to https://github.com/microsoft/microsoft-ui-xaml/issues/9980
If you reference a library that hasn't done the work to upgrade to WinAppSDK 1.6, upgraded CSWinRT and generated the new projections, what you're met with is this obscure error on launch:

There's no way to identify what is causing this crash. If we could have a build error/warning when PublishAoT is enabled, or a better exception at runtime that lets us identify which dependency doesn't support AoT, so that we can contact the library authors and have them address it.

### Steps to reproduce the bug

1. Create a new WinUI3 project and enabled it for AoT
2. Reference WinUIEx v2.4.0
3. Run the app.
4. Boom!

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

WinUI 3 - Windows App SDK 1.6.0: 1.6.240829007

### Windows version

Windows 11 (22H2): Build 22621

### Additional context

_No response_

Start with the WinAppSDK 1.6 PublishAoT reproduction using a new WinUI3 project and WinUIEx v2.4.0. Compare the current launch failure with the requested build warning or runtime exception, and consider the work complete when the unsupported dependency can be identified from the resulting diagnostic.

Written by the indexing model from the issue text.