Move ir box test under "box/ir"

compiler/testData/codegen/box/ir/closureConversion/innerClass1.kt

@@ -0,0 +1,8 @@
+class Outer {
+    val x = "O"
+    inner class Inner {
+        val y = x + "K"
+    }
+}
+
+fun box() = Outer().Inner().y