[Test] Properly merge box against java testdata into codegen/box

Previous commit about it was 3199ce03 and it was completely wrong

compiler/testData/codegen/box/sam/smartCastSamConversion.kt

@@ -0,0 +1,26 @@
+// DONT_TARGET_EXACT_BACKEND: JS JS_IR JS_IR_ES6 WASM NATIVE
+// MODULE: lib
+// FILE: JFoo.java
+public interface JFoo<T> {
+    T foo(T x);
+}
+
+// FILE: J.java
+public class J {
+    public static void use(JFoo<String> jfoo) {
+        jfoo.foo(null);
+    }
+}
+
+
+// MODULE: main(lib)
+// FILE: test.kt
+fun test(a: Any) {
+    a as (String) -> String
+    J.use(a)
+}
+
+fun box(): String {
+    test({s: String? -> s})
+    return "OK"
+}