[v9]: Remove dart:html usage in favour of package:web

[buenaflor]

📜 Description

💡 Motivation and Context

Closes #2411

💚 How did you test it?

Existing 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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.32%. Comparing base (7a0aa9a) to head (de974a7).
Report is 1 commits behind head on v9.

Additional details and impacted files

@@           Coverage Diff           @@
##               v9    #2710   +/-   ##
=======================================
  Coverage   88.32%   88.32%           
=======================================
  Files         262      262           
  Lines        8913     8913           
=======================================
  Hits         7872     7872           
  Misses       1041     1041           

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[denrase]

Lookin' good, except the conflicts.