Dart Debug Extension builder fix

[elliette]

I'm not sure exactly what changed, but it seems like the copy_builder (defined as a builder_factory in our build.yaml file) no longer works as intended. None of the dart.js files were being copied over to /compiled. (Was there a change to build_runner that might have caused this?)

In any case, I've changed the builder logic to:

• initially build everything to /build
• copy over the files that are need to /compiled

[natebosch]

May have been impacted by dart-archive/graphs#86

It's likely that the fix is to add explicit ordering information to some builders.

Can you try adding a required_inputs: [".js",".png", ".html", ".css", ".json"] to the configuration for the copy builder?

You can also check the generated build.dart file in .dart_tool/build/entrypoint/build.dart to confirm that the copy builder is currently earlier in the list than the web compilers.

[elliette]

That worked! Thanks @natebosch

Closing this PR in favor of #2117