Fix #5044: guard against forward references in the TypeTree of New trees

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -1010,9 +1010,14 @@ class RefChecks extends MiniPhase { thisPhase =>
   }
 
   override def transformNew(tree: New)(implicit ctx: Context) = {
-    val sym = tree.tpe.typeSymbol
+    val tpe = tree.tpe
+    val sym = tpe.typeSymbol
     checkUndesiredProperties(sym, tree.pos)
     currentLevel.enterReference(sym, tree.pos)
+    tpe.dealias.foreachPart {
+      case TermRef(_, s: Symbol) => currentLevel.enterReference(s, tree.pos)
+      case _ =>
+    }
     tree
   }
 }
@@ -1643,4 +1648,3 @@ class RefChecks extends MiniPhase { thisPhase =>
       }
     }
 */
-

tests/neg/i5044a.scala

@@ -0,0 +1,7 @@
+class I0 {
+  class I1
+  def i3 = {
+    val i4 = new i5.I1 // error: `i5` is a forward reference extending over the definition of `i4`
+    val i5 = new I0
+  }
+}

tests/neg/i5044b.scala

@@ -0,0 +1,8 @@
+class I0 {
+  class I1
+  def i3 = {
+    type T = i5.I1
+    val i4 = new T // error: `i5` is a forward reference extending over the definition of `i4`
+    val i5 = new I0
+  }
+}