Fixes
- Ref: Deprecate SentryBaseEventgetOriginThrowable and add SentryBaseEventgetThrowableMechanism ([1502](https://github.com/getsentry/sentry-java/pull/1502))
- Graceful Shutdown flushes event instead of Closing SDK ([1500](https://github.com/getsentry/sentry-java/pull/1500))
- Do not append threads that come from the EnvelopeFileObserver ([1501](https://github.com/getsentry/sentry-java/pull/1501))
- Ref: Deprecate cacheDirSize and add maxCacheItems ([1499](https://github.com/getsentry/sentry-java/pull/1499))
- Append all threads if Hint is Cached but attachThreads is enabled ([1503](https://github.com/getsentry/sentry-java/pull/1503))