[VM] Add more information when seeing disagreeing sources in a dill
[VM] Add more information when seeing disagreeing sources in a dill

Hopefully this extra information will help debugging an issue such as
https://github.com/flutter/flutter/issues/60794

Change-Id: I426a9ab50a88f49ded47012a8f0aa280ea7e5ae2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153212
Commit-Queue: Jens Johansen <05223a3c6bdf76af6f84755eae231abeebcf4530@google.com>
Reviewed-by: Martin Kustermann <a35dd5b79fac84b2bb3b026a16b8becc55af5961@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