Surprising scoping behavior: annotations on class properties cannot see the enclosing class

In this snippet, `qux` is not visible inside `@MyAnnotation { ... }`.

```pkl
class MyClass {
@MyAnnotation { prop = qux }
foo: Int

const qux = 15
}
```

Start by reproducing the supplied Pkl snippet and inspect how annotation bodies on class properties resolve names. Trace the scoping rules for `@MyAnnotation { prop = qux }` and compare them with the enclosing class scope. Done means the example can resolve `qux` as the class property, with a regression test covering the behavior.

Written by the indexing model from the issue text.