Better printing of <skolem> prefixes in FreshCaps

 - Print <skolem> and this as prefix only under -Ycc-verbose
 - Compose a "in new instance of class C" owner for skolem prefixes

Author: odersky

compiler/src/dotty/tools/dotc/cc/Capability.scala

@@ -205,6 +205,11 @@ object Capabilities:
         hiddenSet.adoptClassifier(cls)
         if freeze then isClassified = true
 
+    def ccOwnerStr(using Context): String =
+      val owner = ccOwner
+      if owner.name == nme.SKOLEM then i"a new instance of ${hiddenSet.owner}"
+      else owner.show
+
     def descr(using Context) =
       val originStr = origin match
         case Origin.InDecl(sym) if sym.exists =>

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

@@ -492,11 +492,13 @@ class PlainPrinter(_ctx: Context) extends Printer {
         if c.hiddenSet.classifier == defn.AnyClass then ""
         else s" classified as ${c.hiddenSet.classifier.name.show}"
       def prefixTxt: Text = c.prefix match
-        case NoPrefix | _: ThisType => ""
+        case NoPrefix => ""
+        case _: ThisType if !ccVerbose => ""
+        case pre: TermRef if !ccVerbose && pre.name == nme.SKOLEM => ""
         case pre: SingletonType => toTextRef(pre) ~ "."
         case pre => toText(pre) ~ "."
       def core: Text =
-        if ccVerbose then s"<fresh$idStr in ${c.ccOwner} hiding " ~ toTextCaptureSet(c.hiddenSet) ~ classified ~ ">"
+        if ccVerbose then s"<fresh$idStr in ${c.ccOwnerStr} hiding " ~ toTextCaptureSet(c.hiddenSet) ~ classified ~ ">"
         else "cap"
       prefixTxt ~ core
     case tp: TypeProxy =>