Fix object selftype match error (#16441)

Fixes #16437

Author: dwijnand

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1074,6 +1074,7 @@ object SymDenotations {
               case tp: Symbol => sourceOfSelf(tp.info)
               case tp: RefinedType => sourceOfSelf(tp.parent)
               case tp: AnnotatedType => sourceOfSelf(tp.parent)
+              case tp: ThisType => tp.cls
             }
             sourceOfSelf(selfType)
           case info: LazyType =>

tests/pos/i16437/def_1.scala

@@ -0,0 +1,9 @@
+class OU {
+  def dn: String = ""
+}
+
+class Inventory() {
+  object NODES extends OU { nodes =>
+    val x = nodes.dn
+  }
+}

tests/pos/i16437/use_2.scala

@@ -0,0 +1,2 @@
+@main def Test =
+  new Inventory().NODES.dn