[dart2wasm] Correctly deal with abstract members in selector building

When we create a `Selector` we compute various information
based on all members belonging to that selector. Before this
CL this was split up: Some things like `ParameterInfo` was
calculated&updated while discovering members, others was
calculated after all members were discovered.

We now make all fields whose value depends on knowing all
members `late final` and initialize those fields after
having found all members of a selector.

When we compute the `ParameterInfo` of the selector we take
special care:

If there's non-abstract implementations and the selector is
not overridable by dynamic modules then we create the
`ParameterInfo` by looking only at the non-abstract members

=> This increases precision as we ignore the types and
   default values of optional parameters for abstract members

If there's no implementations of the selector it may still be
referred to by instance invocation AST nodes (which are
unreachable). The current code generator still needs a
`Selector.signature` in order to evaluate arguments for such
nodes.

=> We calculate `ParameterInfo` based on the abstract member
   and use `defaultSentinel` for optional parameters.

If a selector can have implementations in dynamic modules
then we cannot determine whether all implementations have
the same default value of optional parameters.

=> We calculate `ParameterInfo` using `defaultSentinel`
   value for all optional parameters. Ensuring the caller
   doesn't pass them but the callee will default to it's
   default value if it wasn't passed by caller.

See added test case for when we (before this CL) may
use unreachable members in the param info / signature
calculation and how that could lead to a compiler bug
(before this CL) due to a missing
 `VariableDeclaration.initializer`

TEST=web/wasm/unreachable_selector_implementation_test

Change-Id: I3628177f8e93c5d24ff0eb0ff8fee6121a4a08d1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/428541
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
4 files changed
tree: 9a1c46b79ec5f481c7de251fa245bc77b323d512
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  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. .style.yapf
  21. AUTHORS
  22. BUILD.gn
  23. CHANGELOG.md
  24. codereview.settings
  25. CONTRIBUTING.md
  26. DEPS
  27. LICENSE
  28. OWNERS
  29. PATENT_GRANT
  30. PRESUBMIT.py
  31. pubspec.yaml
  32. README.dart-sdk
  33. README.md
  34. sdk.code-workspace
  35. sdk_args.gni
  36. sdk_packages.yaml
  37. SECURITY.md
  38. WATCHLISTS
README.md

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