Parsing error with `$_` and `$_id` in interpolated strings

Dotty cannot parse `$_` and `$_id`, while Scalac only supports `$_`.

```Scala
object Test {
  implicit class Foo(sc: StringContext) {
    object q {
      def unapply(arg: Any): Option[(Any, Any)] =
        Some((sc.parts(0), sc.parts(1)))
    }
  }

  def main(args: Array[String]): Unit = {
    val q"class $_ extends $_parent" = new Object
    println(_parent)
  }
}
```