Support iOS BeforeSend and OnCrashedLastRun

[mattjohnsonpint]

For iOS and MacCatalyst targets, the bundled Sentry Cocoa SDK has the BeforeSend and OnCrashLastRun options, both of which should probably be exposed via .NET. They require conversion between the .NET SDK's SentryEvent and the Cocoa SDK's SentryEvent objects.

For Android, we do this via serialization/deserialization. However the Cocoa SDK doesn't currently offer deserialization for SentryEvent, so a similar approach would not work.

The object graphs are quite large, so implementing the conversions manually will take time and a lot of tests.

This was originally planned for MAUI GA, but is deferred for now.

Related issues

• dotnet code setting User.id not showing up in iOS events #3621
• [iOS] Inconsistent event enrichment mechanism #3854