Add a Hint enforcing contract of @literal

Example code:

```dart
import 'package:meta/meta.dart';

class A {
  @literal
  const A();

  @literal
  const A.named();
}

var a = A();
var b = const A();
const c = A();
var d = new A();

var e = new A.named();
```

Produces:

Analyzing b.dart...
  hint • This instance creation must be 'const', because the A constructor is marked as '@literal' at b.dart:11:9 • non_const_call_to_literal_constructor
  hint • This instance creation must be 'const', because the A constructor is marked as '@literal' at b.dart:14:9 • non_const_call_to_literal_constructor
  hint • This instance creation must be 'const', because the A.named constructor is marked as '@literal' at b.dart:16:9 • non_const_call_to_literal_constructor
3 hints found.

Bug: https://github.com/dart-lang/sdk/issues/34259
Change-Id: Iba10e5e0a0b2d0f7e99556cd6c201cea229ad675
Reviewed-on: https://dart-review.googlesource.com/c/88422
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
10 files changed
tree: 8af2466efad69dfe6f3de0e5f6e8d30579af39ee
  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. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. dartdoc_options.yaml
  28. DEPS
  29. LICENSE
  30. PATENTS
  31. PRESUBMIT.py
  32. README.dart-sdk
  33. README.md
  34. WATCHLISTS
README.md

Dart

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