[EPIC] Tag all spans with thread info

[markushi]

For mobile starfish we want to tag all spans, indicating if the ran on the main thread or not.
The main thread flag is determined in the moment the span was started (similar to otel).

See span data conventions https://develop.sentry.dev/sdk/performance/span-data-conventions/#thread on how to add this info.

Tasks

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1. Tag all spans with main thread flag sentry-java#2997
   Platform: Android +1
   
2. Tag all spans with thread info sentry-cocoa#3355
   Platform: Cocoa +1
   
3. Tag all spans with thread info sentry-react-native#4461
   Platform: React-Native +1
4. Tag all spans with thread info sentry-dart#2505
   9.0.0 Blocked Platform: Dart +3

[krystofwoldrich]

What for will this information be used in Sentry? RN has the JS (javascript) and UI (main) threads and both are of high importance for smooth user experience.

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Is the thread.id optional?

[krystofwoldrich]

Since there are no features depending on the names at the moment, RN will use javascript and main.