package:build_test v3.5.0

• Improve TestBuilderResult: add succeeded, outputs and errors.
  Deprecate buildResult in favor of these new members.
• Add verbose to testBuilders and related methods. Like the command line
  flag it enables info logging from builders.
• Add flattenOutput to testBuilders. Use it for a less realistic but simpler
  build in which generated outputs are always written directly to each package
  instead of "hidden" output being written to .dart_tool/build/generated.