Add testcase for #19988

Author: Linyxus

tests/pos/i19988.scala

@@ -0,0 +1,7 @@
+import collection.IndexedSeqView
+object Hello extends App {
+  def foo(view: IndexedSeqView[Int]): Unit =
+    val x1 = 1 +: view
+    val x2 = view :+ 1
+}
+