Remove `sentry` frames if SDK falls back to current stack trace

[denrase]

:scroll: Description

• SDK removes sentry frames if the SDK falls back to StackTrace.current

So we don't say that the app crashed in stacktrace_utils.dart anymore.

Before

After (More frames are hidden in this screenshot, but it's identical to before)

:bulb: Motivation and Context

Relates to #2268

:green_heart: How did you test it?

• Unit tests

:pencil: Checklist

• [x] I reviewed submitted code
• [x] I added tests to verify changes
• [ ] No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• [ ] I updated the docs if needed
• [x] All tests passing
• [x] No breaking changes

:crystal_ball: Next steps

Will this affect grouping as well?

Grouping in Sentry is different for events with stack traces and without. As a result, you will get new groups as you enable or disable this flag for certain events.

Will this affect SDK crash detection, provided we have this functionality on sentry dart/flutter?