`collection.Seq` factory doesn't preserve `collection.Seq`s

[lrytz]

Welcome to Scala 2.13.10 (OpenJDK 64-Bit Server VM, Java 17.0.1).
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scala> import collection.mutable
import collection.mutable

scala> val s: collection.Seq[Int] = mutable.ArraySeq(1)
val s: scala.collection.Seq[Int] = ArraySeq(1)

scala> val es = s.to(collection.Seq)
val es: scala.collection.Seq[Int] = List(1)

scala> es eq s
val res0: Boolean = false

[lrytz]

Hmm, probably that's by design, to can return the same instance for immutable collections, but is otherwise supposed to create a copy.

scala> val s = mutable.ArraySeq(1,2,3)
val s: scala.collection.mutable.ArraySeq[Int] = ArraySeq(1, 2, 3)

scala> s.to(mutable.Seq) eq s
val res1: Boolean = false

[SethTisue]

Pretty sure there was a design discussion about this in not the too distant past, though I don't recall what the outcome was. I can dig for it later. cc @scala/collections

[SethTisue]

Also let's check and make sure that the Scaladoc is totally explicit on this point.