ref: Align SentryException with unified API

[philipphofmann]

📜 Description

Replace SentryException.thread with threadId and stacktrace. This aligns
SentryException with the exception interface, see
https://develop.sentry.dev/sdk/event-payloads/exception/.

💡 Motivation and Context

We want to align the SDK with our spec.

💚 How did you test it?

CI and simulator.

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the CHANGELOG if needed
• I updated the docs if needed
• Review from the native team if needed
• No breaking changes

🔮 Next steps

[codecov-io]

Codecov Report

Merging #1026 (4e9c2eb) into master (c74fc40) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 4e9c2eb differs from pull request most recent head 9d11092. Consider uploading reports for the commit 9d11092 to get more accurate results

@@            Coverage Diff             @@
##           master    #1026      +/-   ##
==========================================
- Coverage   95.31%   95.29%   -0.03%     
==========================================
  Files          92       92              
  Lines        4034     4036       +2     
==========================================
+ Hits         3845     3846       +1     
- Misses        189      190       +1     

Impacted Files	Coverage Δ
Sources/Sentry/SentryCrashReportConverter.m	95.03% <100.00%> (+0.03%)	⬆️
Sources/Sentry/SentryException.m	100.00% <100.00%> (ø)
Sources/Sentry/SentryThreadInspector.m	96.29% <0.00%> (-3.71%)	⬇️

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