Do not access enum symbol in DesugarEnums

Follow up of scala#19182. Using `fullName` causes the the `parallelBackend`
tests to loop forever.

Fixes scala#19285
Fixes scala#19281
Fixes scala#19278

compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala

@@ -126,7 +126,7 @@ object DesugarEnums {
 
     val valuesOfBody: Tree =
       val defaultCase =
-        val msg = Apply(Select(Literal(Constant(s"enum ${enumClass.fullName} has no case with name: ")), nme.PLUS), Ident(nme.nameDollar))
+        val msg = Apply(Select(Literal(Constant(i"enum $rawEnumClassRef has no case with name: ")), nme.PLUS), Ident(nme.nameDollar))
         CaseDef(Ident(nme.WILDCARD), EmptyTree,
           Throw(New(TypeTree(defn.IllegalArgumentExceptionType), List(msg :: Nil))))
       val stringCases = enumValues.map(enumValue =>
@@ -143,12 +143,13 @@ object DesugarEnums {
   }
 
   private def enumLookupMethods(constraints: EnumConstraints)(using Context): List[Tree] =
+    val rawEnumClassRef = rawRef(enumClass.typeRef)
     def scaffolding: List[Tree] =
       if constraints.isEnumeration then enumScaffolding(constraints.enumCases.map(_._2)) else Nil
     def valueCtor: List[Tree] = if constraints.requiresCreator then enumValueCreator :: Nil else Nil
     def fromOrdinal: Tree =
       def throwArg(ordinal: Tree) =
-        val msg = Apply(Select(Literal(Constant(s"enum ${enumClass.fullName} has no case with ordinal: ")), nme.PLUS), Select(ordinal, nme.toString_))
+        val msg = Apply(Select(Literal(Constant(i"enum $rawEnumClassRef has no case with ordinal: ")), nme.PLUS), Select(ordinal, nme.toString_))
         Throw(New(TypeTree(defn.NoSuchElementExceptionType), List(msg :: Nil)))
       if !constraints.cached then
         fromOrdinalMeth(throwArg)