ECJ appears to forego many semantic checks for members of local anonymous classes

Found while working on https://github.com/eclipse-jdt/eclipse.jdt.core/issues/4290

This program which should be rejected is compiled by ECJ:

```
interface I {

}
public class X {
public Object a() {
return new Object() {
static class A implements I, I {}
};
}
}
```

This faulty behaviors has been there for a long time, I could verify it at 4.20 - but it likely dates back even earlier looking the git blame logs.

See https://github.com/eclipse-jdt/eclipse.jdt.core/issues/4290#issuecomment-3194719746
and https://github.com/eclipse-jdt/eclipse.jdt.core/issues/4290#issuecomment-3194795382