Make is a lot easier to enable including source_maps in dart2js output

[kevmoo]

See https://stackoverflow.com/questions/51944375/webdev-serve-missing-output-for-js-map-files

This is the best example we have – crazy - https://github.com/dart-lang/angular_components_example/blob/master/example/angular_components_example/build.yaml

[natebosch]

To be precise, the code it takes to do this is:

global_options:
  build_web_compilers|dart_source_cleanup:
    release_options:
      enabled: false
  build_web_compilers|dart2js_archive_extractor:
    release_options:
      filter_outputs: false

The main difficulty here is:

• having to configure multiple builders
• those builders having inconsistent options that need to be set - enabled vs filter_outputs.

We could solve both of those fairly easy after we implement #1544

[travissanderson-wf]

Unless I am missing something, this is still quite difficult to do

[natebosch]

Unless I am missing something, this is still quite difficult to do

Does the config above work?

[travissanderson-wf]

We use something similar that works in our primary product, but I tried using that in the benchmarks app in https://pub.dev/packages/r_tree and was unsuccessful