Collective extension methods drop annotations

[bishabosha]

minimized code

given fooOps: [A](a: A) with

  @nonsense
  def foo = ???

expectation

Either an error that annotations are not accepted in this position, or a type error because nonsense can't be found

notes

the parser accepts the annotation, as seen by output with Xprint:parser:

parsed:
package <empty> {
  given object fooOps[A](a: A) {
    @nonsense() def foo = ???
  }
}

but it is dropped by the end of frontend

[bishabosha]

This was fixed in #7572 but the linked issue from that was PR incorrect, (but already closed).