Span.toSentryTrace() should use its own spanId

[marandaneto]

https://github.com/getsentry/sentry-java/blob/main/sentry/src/main/java/io/sentry/Span.java#L58-L60

.NET
https://github.com/getsentry/sentry-dotnet/blob/39680350f97cc4c6901f7a0f56d7ad7f2f2aa46a/src/Sentry/Span.cs#L92-L97

[marandaneto]

@maciejwalkowiak let's run a server & client sample and correlate the Ids manually using a transaction and/or an inner span, we should guarantee that this renders correctly on the UI and that the spans are properly connected on the server.