Report Flutter framework feature flags

[ueman]

📜 Description

There's a Flutter framework PR (flutter/flutter#168437, flutter/flutter#171545 (reland of the first PR)) that adds feature flags to Flutter itself.
This PR supports that

💡 Motivation and Context

I want know whether a specific build used one of the feature flags.

💚 How did you test it?

Automated 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

I'll keep this a draft until the linked PR is merged for some time. Afterwards this PR can be landed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.09%. Comparing base (2d34233) to head (8e94480).

❗ There is a different number of reports uploaded between BASE (2d34233) and HEAD (8e94480). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (2d34233)	HEAD (8e94480)
	9	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2991       +/-   ##
===========================================
- Coverage   87.97%   63.09%   -24.89%     
===========================================
  Files         287        4      -283     
  Lines        9533      168     -9365     
===========================================
- Hits         8387      106     -8281     
+ Misses       1146       62     -1084     

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[ueman]

I would still wait with merging this PR until the linked PR is merged

[loic-sharma]

Hello, I'm sure you're aware but this reaches into Flutter internals that aren't meant to be public. This isn't covered by Flutter's breaking change policy. I'd assume the format of FLUTTER_ENABLED_FEATURE_FLAGS can and will change, even in a patch release. The current changes seem reasonable, but I'd consider documenting this so that future contributors are aware as well.