deprecate nested "overriding" classes with same name

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Martin says:

In dotty I propose to no longer allow nested classes with the same name which shadow each other. It's less convenient that way, but a lot safer.

instead of:

trait Core extends Base {
  class Status
}

trait Ext extends Core {
  class Status extends super.Status
}

write:

trait Core extends Base {
  class Status
}

trait Ext extends Core {
  class StatusExt extends Status
}

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Imported From: https://issues.scala-lang.org/browse/SI-8353?orig=1
Reporter: @adriaanm

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@adriaanm said:
See also #7278

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@soc said:
I'd prefer either fixing it and make it a full-blown overriding relationship, or just deprecate and remove nested classes/types altogether. Having completely different rules for classes/types and methods/values is just nuts.

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@adriaanm said:
Neither of these extremes will happen. A language with virtual classes is research territory, and a language without nested classes/types would not be Scala.