When a transaction is finished, the SDK tries to send the data to Sentry.
If an open Span (one that was not finished) exist in that transaction, the SDK removes that span before sending the data to Sentry.

That was done because Sentry will discard the transaction if unfinished spans are included. More context on this thread: getsentry/develop#274

An alternative solution used by the JavaScript SDK is to complete those spans with the timestamp of the finishing transaction and setting the status to timeline_exceeded. We should align with this approach as it shows something was going on even though it wasn't completed during the transaction.

On:

### Tasks
- [ ] https://github.com/getsentry/sentry-cocoa/issues/1303
- [ ] https://github.com/getsentry/sentry-dotnet/issues/1182
- [ ] https://github.com/getsentry/relay/issues/1244
- [ ] https://github.com/getsentry/sentry-dotnet/issues/1182