implement super mixins in dartdevc and fix a few issues in Analyzer

Fixes #34167. This implements the Dart 2 mixin proposal
(https://goo.gl/KEKQyv) for DDC. When the mixin is applied, a class
is created for the application that extends the correct superclass
and has all of the instance members, so `super` works correctly.

This also fixes a few minor issues in Analyzer's (mostly complete)
implementation:
- InterfaceType.isObject now returns false for Dart 2 mixins.
- Least upper bound calculation recognizes mixins are not Object.
- Interface of the mixin now implements its superclass constraints.
- Mixin superclass constraints are checked against the superclass and
  all previously applied mixins (if any); this keeps it working with
  the subtype fix above, and also prevents a not-yet-applied mixin
  from satisfying the constraint

The language_2/mixin_declaration tests were updated with a few minor
fixes now that we can run Analyzer/dartdevc to test them.

This change implements super mixins for DDC's Kernel backend (DDK)
too. This will be enabled once Kernel adds a flag to recognize which
Class nodes are mixins (vs normal classes).


Change-Id: Ib3c4fcb12de9988345e52d92931196828d8227c3
Reviewed-on: https://dart-review.googlesource.com/74965
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Vijay Menon <vsm@google.com>
24 files changed
tree: e767626b4f82dfbcd343274ab3696b1eed446121
  1. .github/
  2. build/
  3. client/
  4. docs/
  5. pkg/
  6. runtime/
  7. samples/
  8. samples-dev/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .packages
  21. AUTHORS
  22. BUILD.gn
  23. CHANGELOG.md
  24. codereview.settings
  25. CONTRIBUTING.md
  26. dartdoc_options.yaml
  27. DEPS
  28. LICENSE
  29. PATENTS
  30. PRESUBMIT.py
  31. README.dart-sdk
  32. README.md
  33. WATCHLISTS
README.md

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