Exception aggregate mechanism

[ueman]

📜 Description

Adds the new field according to https://github.com/getsentry/rfcs/blob/main/text/0079-exception-groups.md#new-mechanism-fields

I didn't yet implement exception aggregates for anything. That can be done in follow-up PRs.
The current CI failures are due to targeting the v8 branch, I believe. At least, I can't see any failures related to the new code.

💡 Motivation and Context

https://github.com/getsentry/rfcs/blob/main/text/0079-exception-groups.md

A tiny step towards #1859

💚 How did you test it?

Updated tests

📝 Checklist

• I reviewed submitted code
• 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
• All tests passing
• No breaking changes

🔮 Next steps

Use it for PlatformException in the Flutter code.

#skip-changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.55%. Comparing base (fab52eb) to head (1cd7fbb).
Report is 245 commits behind head on release/8.0.0.

Additional details and impacted files

@@               Coverage Diff               @@
##           release/8.0.0    #1866    +/-   ##
===============================================
  Coverage          88.55%   88.55%            
===============================================
  Files                205      218    +13     
  Lines               6884     7522   +638     
===============================================
+ Hits                6096     6661   +565     
- Misses               788      861    +73     

☔ View full report in Codecov by Sentry.
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[buenaflor]

some tests are still failing it looks like

[ueman]

@buenaflor
I've fixed the issues. Is the target branch still the correct one, or should I target another branch?

[buenaflor]

release/8.0.0 is fine, thx, I'll merge once everything is green (except sentry-dio, that's expected to fail currently fyi)

[ueman]

@buenaflor Is there something I still need to do here? As far as I can tell, the remaining failing jobs aren't related to this PR.

[buenaflor]

I'll merge main into v8 soon and the ci should be green then