ExplicitOuter failure when calling inline method defined in inner class of superclass

Triggered while trying to compile the shared backend with dotty, here's a minimization:
```scala
class A {
  class Foo {
    inline def inlineMeth: Unit = {
      new Bar
    }
  }
  class Bar
}

class B extends A {
  (new Foo).inlineMeth
}
```