Remove all uses of toIterable in code compiled with Scala 2.13.x.

[sjrd]

It will be deprecated in Scala 2.13.7.

See scala/scala#9774 (not yet reviewed at the time of this writing)

After these changes, the only remaining uses of .toIterable are in code that is 2.11- or 2.12-specific:

$ git grep -w toIterable
library/src/main/scala-old-collections/scala/scalajs/js/WrappedMap.scala:    underlying.asInstanceOf[js.Map.Raw[K, V]].keys().toIterator.toIterable
scalalib/overrides-2.11/scala/collection/immutable/Range.scala:  override def toIterable = this
scalalib/overrides-2.12/scala/collection/immutable/Range.scala:  override def toIterable = this

[NthPortal]

out of curiosity, why does this need to be converted specifically to the less specific JavaCollectionWrappers.IterableWrapper rather than JavaCollectionWrappers.SeqWrapper?

[sjrd]

SeqWrapper seems to be index-based:
https://github.com/scala/scala/blob/207c01b8efa96b9ba556bedcffc13458be2eafbd/src/library/scala/collection/convert/JavaCollectionWrappers.scala#L81
which is not good for a linear collection like List. Explicitly ascribing to Iterable makes it 100% sure that it is going to use a linear implementation.

[NthPortal]

that actually stopped working in 2.13, as toIterable on subtypes of Iterable[_] was changed to return this.type