Don't eta expand when reading Scala 2 types

Eta expansion needs type parameters which can provoke a cycle.

Fixes #12109.

Author: odersky

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -792,7 +792,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
           OrType(args(0), args(1), soft = false)
         }
         else if (args.nonEmpty) tycon.safeAppliedTo(EtaExpandIfHK(sym.typeParams, args.map(translateTempPoly)))
-        else if (sym.typeParams.nonEmpty) tycon.EtaExpand(sym.typeParams)
+        //else if (sym.typeParams.nonEmpty) tycon.EtaExpand(sym.typeParams)
         else tycon
       case TYPEBOUNDStpe =>
         val lo = readTypeRef()

tests/pos/i12109/JsonReaderDefaultValue.scala

@@ -0,0 +1,8 @@
+object JsonReaderDefaultValue extends LowPriorityDefaultValue {
+  class ReaderDefaultValue extends scala.annotation.StaticAnnotation
+}
+
+trait LowPriorityDefaultValue {
+  @JsonReaderDefaultValue.ReaderDefaultValue
+  class NoDefaultValue
+}

tests/pos/i12109/Test.scala

@@ -0,0 +1,3 @@
+object Test {
+  JsonReaderDefaultValue
+}