Regression test for 21360 (scala#21591)

Closes scala#21360 

@dwijnand This might have been fixed by your recently merged changes to
constructor completion.

Author: odersky

tests/pos/i21360.scala

@@ -0,0 +1,11 @@
+case class Table(owner: Owner.Id)
+
+case class Owner(owner: Owner.Id) // type Id is not a member of object Playground.Owner
+
+trait Typed[Tag] {
+  type Id = String
+}
+
+object Owner extends Typed[Owner] {
+  //type Id = String
+}