Dwds build runner tests (#2879)

Delete `dwds` and `dwds_test_common` and move build daemon tests to `dwds_webdev_integration_test`

`dwds` and `dwds_test_common` now live in the Dart SDK (`pkg/dwds` and `pkg/dwds_test_common`) and will be published from there.

- Move the DWDS `build_runner` / build daemon integration tests into a new
  unpublished `dwds_webdev_integration_test` package that runs against the
  shared test harness in `dwds_test_common`.
- Delete `dwds/` and `dwds_test_common/`, and point the repo `README.md` at the
  Dart SDK's copy of `dwds`.
- Update `webdev` to depend on `dwds_test_common` solely via the SDK git
  override, copy the `_webdev_smoke` fixture from the resolved package into a
  temp directory for e2e/TLS tests, and verify that the fixture's SDK constraint
  allows all SDK versions supported by `webdev`.
- Update CI workflows, `mono_repo` configuration, and labeler globs to run
  `dwds_webdev_integration_test` in place of `dwds` and `dwds_test_common`, and
  remove the DWDS-only Dart Code Metrics workflow.