ce0e5c4330
This changes the mapping for the Dart SDK inside Flutter from `org-dartlang-sdk:///third_party/dart/sdk` to org-dartlang-sdk:///flutter/third_party/dart/sdk`. This URI changed in https://github.com/flutter/engine/pull/51917 but was not caught by tests because they only tested a specific set of mappings and there were no integration tests checking what URIs were actually produced by a running app. So, this change also adds an integration tests that ensures that a real running app produces URIs that are then correctly mapped. Fixes https://github.com/Dart-Code/Dart-Code/issues/5164.