Move ir box test under "box/ir"

compiler/testData/codegen/box/ir/closureConversion/closureConversion3.kt

@@ -0,0 +1,11 @@
+fun foo(x: String): String {
+    fun bar(y: String): String {
+        fun qux(z: String): String =
+                x + y + z
+        return qux("")
+    }
+    return bar("K")
+}
+
+fun box(): String =
+        foo("O")