MAUI events become extra context in Sentry events

[mattjohnsonpint]

Continues #1651

• Hook into MAUI events (adds breadcrumbs for now, will add spans for tracing support later)
  • We still will need to do more work here to reduce the number of breadcrumbs sent to those that are meaningful only, include additional data for some events where useful, and remove some data items that might contain PII.

Also:

• Hooks the Microsoft.UI.Xaml.Application.UnhandledException handler when targeting Windows
• Fixes the previous workaround in the sample app's csproj, so it runs on iOS and maccatalyst without crashing
• Adds a workaround that lets unhandled exceptions (crashes) be caught properly for iOS and maccatalyst.
• Registers a Disposer that will ensure the Sentry SDK is disposed with the ServiceProvider, so we flush events to Sentry during shutdown.