Isolate IExceptionFilter and ISentryEventExceptionProcessor failures #5684

Part of #5634.

Branch: main. No public API change, so this doesn't need to wait for v7.

IExceptionFilter.Filter (SentryClient.cs:449) and ISentryEventExceptionProcessor.Process (SentryClient.cs:364-367) have no try/catch of their own. A throw ends in SentryClient.CaptureEvent's catch-all (SentryClient.cs:84). The event is dropped and nothing is counted. The log, An error occurred when capturing the event '{0}'., doesn't name the callback.

That misses the hooks spec's MUST (log an error naming the callback) and its SHOULD (record callback_error). It's a managed-only fix, following the per-processor catch in SentryEventHelper.ProcessEvent.