Fixes #24056 Dealias value class types in structural access

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

@@ -245,7 +245,7 @@ trait Dynamic {
           if tpe.classSymbol.isDerivedValueClass && qual.tpe <:< defn.ReflectSelectableTypeRef then
             val genericUnderlying = ValueClasses.valueClassUnbox(tpe.classSymbol.asClass)
             val underlying = tpe.select(genericUnderlying).widen.resultType
-            New(tpe.widen, tree.cast(underlying) :: Nil)
+            New(tpe.widen.dealias, tree.cast(underlying) :: Nil)
           else
             tree
         maybeBoxed.cast(tpe)

tests/pos/i24056.scala

@@ -0,0 +1,8 @@
+trait DFBit
+final class DFVal[+T, +M](val value: Int) extends AnyVal
+type DFValOf[+T] = DFVal[T, Any]
+
+class Top:
+  val dmn1 = new scala.reflect.Selectable:
+    val o: DFValOf[DFBit] = ???
+  val x = dmn1.o

tests/run/i24056.scala

@@ -0,0 +1,13 @@
+trait DFBit
+final class DFVal[+T, +M](val value: Int) extends AnyVal
+type DFValOf[+T] = DFVal[T, Any]
+
+class Top:
+  val dmn1 = new scala.reflect.Selectable:
+    val o: DFValOf[DFBit] = DFVal(42)
+  val x: DFValOf[DFBit] = dmn1.o
+
+object Test:
+  def main(args: Array[String]): Unit =
+    val t = Top()
+    assert(t.x.value == 42)