[dart2js] handle synthesized parameters in dump-info
[dart2js] handle synthesized parameters in dump-info

Fixes https://github.com/dart-lang/sdk/issues/41459

Change-Id: I70fbe7ebcc79a948d23846cdb756cde77e9db230
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143720
Reviewed-by: Mayank Patke <e0355b78204b67a55a952941c68c8f1b40235938@google.com>
Commit-Queue: Sigmund Cherem <beaea8fd7d2a56555046ba4f362c8a93e3938576@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk