Improve verbose printing of capture sets

Author: odersky

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -171,7 +171,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
       val core: Text =
         if !cs.isConst && cs.elems.isEmpty then "?"
         else "{" ~ Text(cs.processElems(_.toList.map(toTextCapability)), ", ") ~ "}"
-           //     ~ Str("?").provided(!cs.isConst)
+           ~ Str("?").provided(ccVerbose && !cs.isConst)
+           ~ Str(s"#${cs.asVar.id}").provided(showUniqueIds && !cs.isConst)
       core ~ cs.optionalInfo
 
   private def toTextRetainedElem[T <: Untyped](ref: Tree[T]): Text = ref match