fix(dart): Route SDK diagnostic logs to browser console on web

[theprantadutta]

📜 Description

Splits the default output for SentryInternalLogger into platform-specific implementations selected via the existing _io_* / _web_* companion-file pattern (already used by _io_platform.dart / _web_platform.dart, origin_io.dart / origin_web.dart, dart_exception_type_identifier_io.dart / _web.dart, etc.):

• _io_default_log_output.dart keeps the existing dart:developer.log behaviour on the VM, so DevTools and IDE log views are unchanged.

• _web_default_log_output.dart forwards to window.console.* via package:web, mapping SentryLevel to the matching console method:

  SentryLevel	console.*
  fatal / error	console.error
  warning	console.warn
  info	console.info
  debug	console.debug

💡 Motivation and Context

dart:developer.log does not surface in the browser dev console on Flutter Web, so SDK diagnostic messages (the ones gated by options.debug = true) were silently dropped during web development.

I deliberately used package:web console.* instead of print, to address @buenaflor's concern from the issue thread:

"Something we need to be careful of is that we have an integration that reports prints as breadcrumbs, I want to make sure we don't spill out internal prints as breadcrumbs."

Sentry's print-breadcrumb integration installs a ZoneSpecification(print:) hook inside runZonedGuarded and records every print call as a Breadcrumb. If the SDK's own internal diagnostic logger went through print, every internal line would feed back as a user-visible breadcrumb on captured events. Calling console.* directly bypasses that hook entirely.

Additionally, RuntimeChecker.kDebugMode already short-circuits the logger at the top of _log(), so the whole code path is tree-shaken from release builds regardless of platform — providing a second layer of safety against the breadcrumb-feedback scenario even if a future integration changes how print is intercepted.

Closes #3043

💚 How did you test it?

• Added packages/dart/test/utils/default_log_output_test.dart with two tests for the IO path: (a) it never produces output via print (so the same property holds for the web path, which uses console.*); (b) it accepts all SentryLevels without throwing.
• Added a routing test to internal_logger_test.dart that verifies the conditional import resolves to the IO file on the VM (no print output when logging through the public SentryInternalLogger).
• Verified the web target compiles cleanly: dart compile js -o build/main.dart.js web/main.dart in packages/dart/example_web/ succeeds with the new conditional import in place.
• The existing 25 internal_logger_test.dart tests still pass.
• dart analyze --fatal-warnings on packages/dart/ — clean.

The web console.* behaviour itself is not unit-tested on the VM (the web file can't be exercised there); the example_web compile path provides the static-typecheck guarantee, and a Flutter Web app with options.debug = true would surface the diagnostic logs at the appropriate severity in the dev console.

📝 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 (no doc changes — internal logger format)
• All tests passing (existing + new)
• No breaking changes (purely an additive platform split; VM behaviour unchanged)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.96%. Comparing base (87fcdd8) to head (8263aa5).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3698   +/-   ##
=======================================
  Coverage   86.96%   86.96%           
=======================================
  Files         335      336    +1     
  Lines       11976    11978    +2     
=======================================
+ Hits        10415    10417    +2     
  Misses       1561     1561           

Flag	Coverage Δ
sentry	86.77% <100.00%> (+<0.01%)	⬆️
sentry_dio	97.73% <ø> (ø)
sentry_drift	93.57% <ø> (ø)
sentry_file	65.29% <ø> (ø)
sentry_firebase_remote_config	100.00% <ø> (ø)
sentry_flutter	91.52% <ø> (ø)
sentry_hive	77.48% <ø> (ø)
sentry_isar	74.37% <ø> (ø)
sentry_link	21.50% <ø> (ø)
sentry_logging	97.01% <ø> (ø)
sentry_sqflite	88.81% <ø> (ø)
sentry_supabase	97.27% <ø> (ø)

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[buenaflor]

lgtm 👍

[buenaflor]

I'll rerun some of the tests later, seems like CI is acting up