Are setter names in the scope of an imported or exported library?

The following code is considered erroneous by both the analyzer and the CFE, despite there being a setter named `x` declared in `lib1.dart`. The spec implies that this introduces a name `x=` into the scope, so I would expect that such a name could be shown/hidden. Is this WAI, or is this a bug in the tooling?

```dart
import "lib1.dart" show x=;

export "lib1.dart" show x=;
```

cc @eernstg @munificent @lrhn

Start with the specification passage about setter names in import and export scopes, then reproduce the lib1.dart example with both the analyzer and the CFE. Compare their diagnostics with the spec's treatment of `x=` and determine whether the behavior is intended or requires coordinated specification and tooling changes.

Written by the indexing model from the issue text.