[dart2js] Update test-matrix to specify the libraries.json to dart2js batch runner
[dart2js] Update test-matrix to specify the libraries.json to dart2js batch runner

When multiple experiments are specified, we need to compile the sdk from sources
and the default libraries.json points to the legacy sdk.

Change-Id: I92904e422eb5225372e109ccb4f06b4a54030496
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/141161
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