Improve handling of SDK.handled values as a lot of events have "--" instead of a value

[Angelodaniel]

https://demo.sentry.io/issues/5767541123/?project=1801383&query=is%3Aunresolved+issue.priority%3A%5Bhigh%2C+medium%5D&referrer=issue-stream&statsPeriod=14d&stream_index=0

Android Eng(Stefano): This should be better managed by the backend, and it would affect all the SDKs
One note, though
In our auto-instrumentation we always set it handled to true/false, and we even set it to false when it crashes the app.
There is only one case when we don’t set the flag, or at least only one i can think about now: when the user creates the event, which means it is handled

So I'd say we need to re-evaluate the default behaviour in all of these cases as there are still plenty of issues that have "--" instead of yes/no.