Fix #8846: Add regression test

Author: nicolasstucki

tests/pos/i8846.scala

@@ -0,0 +1,12 @@
+package example
+
+class X(a: => Any)
+
+class XImpl(
+  param: Int
+) extends X({
+    def helper(): AutoCloseable = new AutoCloseable {
+      def close() = println(param)
+    }
+    helper()
+  })